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Rapid detection of heparin-binding protein (HBP) is essential for timely intervention in sepsis cases. Current detection techniques are usually antibody-based immunological methods, which have certain problems, such as complexity and slow detection, and fall short in meeting the urgency of clinical needs. The application of an aptamer can address these concerns well. In this study, HBP-specific DNA aptamers were screened first. Among which, Apt-01, Apt−02, and Apt−13 had a high affinity for HBP, exhibiting impressive KD values of 3.42, 1.44, and 1.04 nmol/L, respectively. Then, the aptamer of HBP and its partially complementary primer probe were combined to form double-stranded DNA (dsDNA) and synthesize a circular DNA template. The template is complementary to the primer probe, but due to the presence of dsDNA, ExoIII cleaves C2-13 as an RCA primer probe, rendering the template unable to recognize the primer probe and preventing the RCA reaction from proceeding. When the target is present, it competes with the adapter for recognition and releases C2-13, exposing its 3′ end. After initiating the RCA at room temperature and reacting with SYBR GreenII at 37 °C for 20 min, fluorescence changes can be observed and quantitatively analyzed at a 530 nm wavelength, achieving quantitative biological analysis. Apt-01 was used to develop a fluorescent biosensor for HBP detection, which exhibited a good linear range (0.01 nmol/L to 10 nmol/L) and detection limit (0.0056 nmol/L). This advancement holds the potential to lay a solid groundwork for pioneering sensitive and specific methods for HBP detection and to significantly enhance the diagnostic processes for sepsis. [ABSTRACT FROM AUTHOR]

Electrochemiluminescence nanoprobes with a core–shell–shell structure have been designed and applied for hyaluronidase detection. The nanoprobes can precipitate efficiently through target-regulation wettability for collection, and enrich near to the hydrophobic electrode surface through hydrophobic interaction to enhance the performance of the biosensor. [ABSTRACT FROM AUTHOR]

The great selectivity and trans-cleavage activity of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas13a had been coupled with high amplification efficiency of hybridization chain reaction (HCR) and magnetic-assisted enrichment, high sensitivity of electrochemiluminescence (ECL) detection to develop an ultra-sensitive biosensor for microRNA-21 (miRNA-21). The CRISPR/Cas13a was used to recognize target RNA with high specificity and performed the trans-cleavage activity. An initiation strand was generated to bind to the probe on the surface of nanomagnetic beads and then trigged HCR to produce long double-strand DNAs (dsDNAs) to realize signal amplification. Ru(phen)32+ can be inserted in the groove of the dsDNAs and acts as the ECL indicator, which can be separated through magnetic enrichment and allowed the platform to reduce the signal background. Under the optimized conditions, there is a good linear correlation between the ECL intensity and the logarithm of miRNA-21 concentration in the range 1 fM–10 nM; the limit of detection (LOD) was 0.53 fM. The proposed system was applied to detect miRNA-21 from the urine of acute kidney injury (AKI) patients with good results. [ABSTRACT FROM AUTHOR]

Gold nanoparticles (AuNPs) in aggregated state have a strong near infrared region (NIR) absorption and the causes a much stronger photothermal effect than that of the dispersed AuNPs. Strand-displacement amplification (SDA) can produce large amount of single-stranded DNA (ssDNA), which in turn effectively prevent AuNPs from aggregation. In this study, these characteristics had been applied to design a photothermal biosensor for human papilloma virus (HPV and HPV16 were chosen as model target) detection. In the absence of HPV16, AuNPs was in the aggregated state and large temperature rise can be detected after the irradiation by 808 nm laser. The presence of HPV16 triggers the SDA reaction with the help of Bst DNA polymerase and Nt.BstNBI nicking endonuclease resulting in the production of large amounts of ssDNA; this protects unmodified AuNPs from salt-induced aggregation. Therefore, AuNPs was in a dispersed state and the temperature change was not significant after the irradiation of 808 nm laser. The difference of the temperature changing can be applied for the quantitative detection of HPV16 using a thermometer as readout. The linear response range is 1.0 fM ~ 50 pM with a detection limit of 0.3 fM. The proposed method has been applied to detect HPV16 in clinical cervical sample and is competent for clinical analysis. [ABSTRACT FROM AUTHOR]

Target-induced differences in the electrostatic interactions between methylene blue (MB) and indium tin oxide (ITO) electrode surface was firstly employed to develop a homogeneous electrochemical biosensor for flap endonuclease 1 (FEN1) detection. In the absence of FEN1, the positively charged methylene blue (MB) is free in the solution and can diffuse onto the negatively charged ITO electrode surface easily, resulting in an obvious electrochemical signal. Conversely, with the presence of FEN1, a 5′-flap is cleaved from the well-designed flapped dumbbell DNA probe (FDP). The remained DNA fragment forms a closed dumbbell DNA probe to trigger hyperbranched rolling circle amplification (HRCA) reaction, generating plentiful dsDNA sequences. A large amount of MB could be inserted into the produced dsDNA sequences to form MB-dsDNA complexes, which contain a large number of negative charges. Due to the strong electrostatic repulsion between MB-dsDNA complexes and the ITO electrode surface, a significant signal drop occurs. The signal change (ΔCurrent) shows a linear relationship with the logarithm of FEN1 concentration from 0.04 to 80.0 U/L with a low detection limit of 0.003 U/L (S/N = 3). This study provides a label-free and homogeneous electrochemical platform for evaluating FEN1 activity. [ABSTRACT FROM AUTHOR]

Hydrogen sulfide (H2S) in joint fluid acts as a signal molecule to regulate joint inflammation. Direct detection of H2S in joint fluid is of great significance for the diagnosis and treatment of arthritis. However, due to the low volume of joint fluid and low H2S concentration, existing methods face the problem of the insufficient limit of detection. In this study, a highly sensitive biosensor was proposed by designing a primer probe and combining it with hybrid chain reaction (HCR) under the strong interaction between metal ions and H2S to achieve H2S detection. The primer probe containing multiple cytosine (C) sequences was fixed on a gold electrode, and the C–Ag–C hairpin structure was formed under the action of Ag+. In the presence of H2S, it can combine with Ag+ in the hairpin structure to form Ag2S, which leads to the opening of the hairpin structure and triggers the hybridization chain reaction (HCR) with another two hairpin structures (H1 and H2). A large number of double-stranded nucleic acid structures can be obtained on the electrode surface. Finally, Ru(phen)32+ can be embedded into the double chain structure to generate the electrochemiluminescence (ECL) signal. The linear response of the H2S biosensor ranged from 0.1000 to 1500 nM, and the limit of detection concentration of H2S was 0.0398 nM. The developed biosensor was successfully used to determine H2S in joint fluid. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) plays a vital role in clinical diagnoses and biomedical research. It is important to develop some convenient but sensitive methods for ALP activity detection. In this study, a multicolor biosensor for ALP activity has been developed based on the peroxidase activity of copper nanoclusters (CuNCs) and etching of gold nanorods (AuNRs). The presence of CuNCs can catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to produce blue TMB+. In acid solution, TMB+ can cause the etching of AuNRs accompanied by a significant color change of the system. The presence of sodium pyrophosphate (PPi) can inhibit the peroxidase activity of CuNCs, which can be recovered after the addition of ALP. Different ALP added results in the recovery of the catalytic activity of CuNCs to different degrees and generates different amounts of TMB+. This consequently affected the morphology of the AuNRs in the system and results in the output of a vivid color change, which can be recognized with the naked eyes easily without any complicated instruments. The biosensor has a linear relationship with ALP activity in the range of 10.0–80.0 U L−1, and the detection limit is 4.6 U L−1. The proposed method has been applied to detect ALP activity in human serum samples with satisfactory results. [ABSTRACT FROM AUTHOR]

MicroRNAs can serve as biomarkers for many cancers, so it is significant to develop simple and sensitive strategies for microRNAs detection. Photoelectrochemical (PEC) detection has the advantages of simple equipment and high sensitivity. But in conventional PEC DNA sensors, tedious immobilization procedures of photoactive materials and capture probes on electrode surfaces are inevitable. To overcome those limitations, a homogeneous PEC biosensor based on target-responsive hydrogels has been developed (miRNA-155 has been chosen as a model target). PEC signal molecules (TiO2 nanoparticles, TiO2 NPs) were embedded in DNA hydrogels formed by hyaluronic acid sodium salt, amine-modified DNA double strands, and polyethylenimine rich in amine groups. In the presence of the target, DNA double strands in hydrogel were nicked by endonuclease and TiO2 NPs were released to the supernate and a high PEC response was obtained when collecting the supernate for PEC test, while almost no TiO2 NPs released in the absence of the target. Thanks to the exonuclease III and nicking endonuclease Nb.BbvCI-assisted cascaded amplification strategy, the proposed biosensor exhibits high sensitivity toward miRNA-155 with a low detection limit of 0.41 fM and a wide linear range from 1.0 fM to 100 pM. Since this method circumvents tedious electrode modification procedures, the proposed technique exhibits the advantages of simplicity and good reproducibility. Moreover, the prepared hydrogels have outstanding storage stability, so that they can be prepared in advance and shorten detection time. This biosensing platform provides a versatile strategy for the construction of homogeneous PEC biosensors for the detection of diverse targets. [ABSTRACT FROM AUTHOR]

Infectious diseases are a long-standing and severe global public health problem. The rapid diagnosis of infectious diseases is an urgent need to solve this problem. MicroRNA (miRNA) plays an important role in the intervention of some infectious diseases and is expected to become a potential biomarker for the diagnosis and prognosis of infectious diseases. It is of great significance to develop rapid and sensitive methods for detecting miRNA for effective control of infectious diseases. In this study, a simple and highly sensitive homogeneous electrochemical method for microRNAs using enzyme-driven cascaded signal amplification has been developed. In the presence of target miRNA, the reaction system produced plenty of MB-labeled single-nucleotide fragments (MB-MF) containing a few negative charges, which can diffuse to the negative surface of the ITO electrode easily, so an obvious electrochemical signal enhancement was obtained. Without the target, MB-HP contains a relatively large amount of negative charges due to the phosphates on the DNA chain, which cannot be digested by the enzyme and cannot diffuse freely to the negatively charged ITO electrode, so only a small signal was detected. The enhanced electrochemical response has a linear relationship with the logarithm of miRNA concentration in the range of 10 fM to 10 nM and the limit of detection as low as 3.0 fM. Furthermore, the proposed strategy showed the capability of discriminating single-base mismatch and performed eligibly in the analysis of miRNA in cell lysates, exhibiting great potential for disease diagnosis and biomedical research. [ABSTRACT FROM AUTHOR]

The change in hyaluronidase (HAase) is related to specific changes in the structure of vitreous, and it is necessary to develop simple but sensitive methods for HAase detection. In this work, a thin film fabricated from a hyaluronic acid (HA)-polyethyleneimine (PEI) hydrogel has been covered on a mixed cellulose microporous membrane (MCEM) to form a HA-PEI-MCEM firstly and it was then applied in a filtration system. The permeability of the filter membrane greatly affects the amount of water passing through within a certain time and the water can be collected and quantitatively measured with a simple electronic balance easily. The low permeability of the HA-PEI-MCEM allows a small amount of water to be drained. But after the addition of HAase, which can hydrolyze HA in the hydrogel, the permeability of the membrane increased. Therefore, the amount of water passing through the HA-PEI-MCEM composite membrane increased accordingly. The composite of the membrane, and the reaction conditions after the addition of HAase were optimized. Under the optimized conditions, the amount of water collected within 5 min showed a linear relationship with the HAase concentration in a range of 1.0–36 U mL−1 with a limit of detection of 0.35 U mL−1.The proposed method has been applied to detect HAase in vitreous samples with satisfactory results. [ABSTRACT FROM AUTHOR]

CD44 is a promising biomarker in the diagnosis and prognosis of malignancies. The serum CD44 level is closely related to disease progression and metastasis of malignancies. It is of great clinical significance for the detection of serum soluble CD44. In this study, a facile, label-free aptamer based electrochemical impedance sensor for serum CD44 has been proposed. The aptamer showing high affinity to CD44 was immobilized on the gold electrodes through Au–S interaction. The interaction between target CD44 and the immobilized aptamer will cause a complex structure change of the aptamer, which makes the diffusion of [Fe(CN)6]3−/4− toward the electrode surface easy, thus resulting in the decrease of the impedance of the system. The decreased degree of the impedance had a good linear relationship with the logarithm of the CD44 concentration in the range of 0.1–1000 ng mL−1 with a detection limit of 0.087 ng mL−1 (S/N = 3). The developed biosensor has been applied to detect CD44 in serum samples with satisfactory results. [ABSTRACT FROM AUTHOR]

A highly sensitive homogeneous electrochemiluminescence (ECL) biosensor for folate receptor (FR) has been developed based on hyperbranched rolling circle amplification (HRCA) and terminal protection. FR was combined to folic acid modified single stranded DNA (FA‐ssDNA) through the strong affinity between FA and FR, which prevented ssDNA from enzymolysis of exonuclease I (Exo I). The protected ssDNA was then applied as a template of padlock looping to trigger the HRCA proceeding. The products of HRCA contains large amount of double strand DNA (dsDNA), which provided excellent carries for Ru(phen)32+ intercalation. The extra free Ru(phen)32+ was removed by ultrafiltration and the Ru(phen)32+ embedded into dsDNA can act as a high‐efficiency ECL indicator to quantify the FR concentration. The enhanced ECL intensity had a linear relationship with logarithm of FR concentration in the range of 4 fM to 120 pM with a correlation coefficient of 0.998. Furthermore, the proposed ECL biosensor has been applied to detect FR in Hela cells and showed a linear relationship with the logarithm of cell concentration ranging from 100–5000 cell/mL. Compared to other FR biosensors, the proposed ECL biosensor presents the merits of the simplicity, high sensitivity and specificity, which shows the great potential application in the field of early cancers diagnosis. Let there be light: an electrochemiluminescence (ECL) biosensor for detection of the folate receptor is fabricated in a homogeneous system. The combination of an effective ECL indicator (Ru(phen)32+) and the hyperbranched rolling circle amplification (HRCA) technique promotes the high sensitivity of the fabricated biosensor. [ABSTRACT FROM AUTHOR]

Bisphenol A (BPA), a typical endocrine disruptor, is widely used as a key monomer in the packaging industry. Residual monomer can transfer from the package material to the food and thereby pose a risk to the health of the consumer, so determination of BPA migration is highly important for food safety control. In this study, a simple but sensitive electrochemiluminescence (ECL) biosensor, which combines the characteristics of high selectivity of an aptamer and high sensitivity of ECL, has been developed to detect BPA from package materials. The aptamer was immobilized on a gold electrode surface through Au-S interaction. The aptamer was then hybridized with complementary DNA (CDNA) to form double-stranded DNA (dsDNA). Ru(phen) can intercalate into the grooves of dsDNA and acts as an ECL indicator; high ECL intensity can therefore be detected from the electrode surface. In the presence of BPA, which can competitively bind with the aptamer owing to their high affinity, Ru(phen) is released from the electrode surface and the ECL of the system is decreased. The decreasing ECL signal has a linear relationship with BPA in the range of 0.1-100 pM with a detection limit of 0.076 pM. The developed biosensor has been applied to detect migration of BPA from different categories of canned drink with satisfactory results. [ABSTRACT FROM AUTHOR]

The authors describe a biosensor for histidine that is based on the use of a DNAzyme catalytic beacon. The Cu(II)-dependent DNA-cleaving DNAzyme (Cu-Enzyme) was modified with a quencher (BHQ1) at its 5′ end, and the corresponding substrate strand (Cu-Sub) was modified with a quencher and the FAM fluorophore at its 5′ and 3′ ends, respectively. The green FAM emission of the system is completely quenched after the Cu-Enzyme is hybridized with Cu-Sub. The presence of Cu(II) triggers the cleavage of the Cu-Sub so that fluorescence recovers. Histidine forms a complex with Cu(II) ion. The complex is not capable of cleaving Cu-Sub effectively so that the fluorescence of the system is not restored. These findings were exploited to design a robust and sensitive assay for the determination of histidine. Fluorescence intensity is linearly related to the concentration of histidine in the range between 0.05 and 40 μM, and the detection limit is 20 nM. The method has been successfully applied to the determination of histidine in (spiked) human urine and gave satisfying results. [ABSTRACT FROM AUTHOR]

Herein, an electrochemiluminescence (ECL) biosensor for ultrasensitive and specific detection of Kras mutant genes has been developed on the basis of the high discrimination capability of locked nucleic acid (LNA) and dual signal amplification techniques including DNA walkers and hyperbranched rolling circle amplification (HRCA). [ABSTRACT FROM AUTHOR]

A highly sensitive and selective fluorescence biosensor for inorganic pyrophosphatase (PPase) activity has been developed based on special click ligation trigger hyperbranched rolling circle amplification (CLT-HRCA). Pyrophosphate ion (PPi) can coordinate with Cu to form stable PPi/Cu complex and Cu in the complex cannot be reduced to Cu. The addition of PPase causes the hydrolysis of PPi into orthophosphate (Pi) and therefore induces the releasing of Cu from the stable PPi/Cu complex, and the free Cu is easily reduced to Cu by sodium ascorbate. Then Cu catalyzes the cyclization reaction between the specially designed 5′-azide and 3′-alkyne tagged padlock probes through Cu catalyzed azide-alkyne cycloaddition (CuAAC), which in turn initiates the hyperbranched rolling circle amplification (HRCA). Given that the CLT-HRCA products contain large amounts of double-stranded DNAs (dsDNAs), the addition of SYBR Green I resulted in the enhanced fluorescence signal. There was a linear relationship between the enhanced fluorescence intensity and the logarithm PPase activity ranging from 0.05 to 25 mU with a detection limit of 0.02 mU. Such proposed biosensor has been successfully applied to screen the potential PPase inhibitors and has accessed the related inhibit ability with high efficiency. [ABSTRACT FROM AUTHOR]

In this study, a hyperbranched rolling circle amplification (HRCA)-based colorimetric biosensor for carcinoembryonic antigen (CEA) is developed with high sensitivity and specificity. A CEA aptamer can bind with its target (CEA) to form a complex due to their high affinity, and the introduced CDNA cannot hybridize with the aptamer. Thus, free CDNA can propagate the HRCA reaction to form a large number of single-stranded DNA (ss-DNA). ss-DNA can be easily adsorbed onto AuNPs and prevent salt-induced AuNPs aggregation, which causes the change in the color of the system. It is found that the absorbance intensity ratio (A520/A660) has a linear relationship with the concentration of the target in the range of 5 pM−0.5 nM, and the detection limit is as low as 2 pM (S/N = 3). [ABSTRACT FROM AUTHOR]

A simple, cost-efficient, sensitive and selective fluorescence sensor is developed for sequence-specific recognition of duplex DNA (ds-DNA) in vitro using metal–organic framework (MOF) as the sensing platform. N,N-Bis(2-hydroxy-ethyl)dithiooxamidatocopper(ii) (H2dtoaCu) was chosen as the example MOF, because it strongly chemisorbs the dye-labeled probe TFO (triplex-forming oligonucleotide), and quenches fluorescence from the dye. In the presence of target ds-DNA (the PPT of HIV RNA, a 16-bp ds-DNA sequence), the TFO could interact with the major groove in ds-DNA (via Hoogsteen hydrogen bonding) to form a rigid triplex structure, resulting in fluorescence recovery. The enhanced fluorescence signal has a relationship with the ds-DNA concentration, the detection limit is as low as 1.3 nmol L−1 (S/N = 3) with good selectivity, which is lower than that based on a graphene oxide platform and electrochemical-DNA sensor. [ABSTRACT FROM AUTHOR]

Abstract: In this study, an electrochemical impedance biosensor for cyanobacterial toxin microcystin-LR (MC-LR) detection has been developed. MC-LR aptamers were immobilized on the gold electrode through Au–S interaction, in the presence of target (MC-LR); the binding of MC-LR and aptamers probe led to a complex formation change on the electrode surface and resulted in the impedance decreasing. The decrease rate had a linear relationship with logarithm of the MC-LR concentration in the range of 1.0×10−7–5.0×10−11 mol/L, with a detection limit of 1.8×10−11 mol/L. The sensor has good selectivity and stability, it has been applied to detect MC-LR in three kinds of real water samples with satisfying results. [Copyright &y& Elsevier]

Abstract: A poly(nickel(II) tetrasulfophthalocyanine)/multi-walled carbon nanotubes composite modified electrode (polyNiTSPc/MWNTs) was fabricated by electropolymerization of NiTSPc on MWNTs-modified glassy carbon electrode (GCE). The modified electrode was found to be able to greatly improve the emission of luminol electrochemiluminescence (ECL) in a solution containing hydrogen peroxide. Glucose oxidase (GOD) was immobilized on the surface of polyNiTSPc/MWNTs modified GC electrode by Nafion to establish an ECL glucose sensor. Under the optimum conditions, the linear response range of glucose was 1.0×10−6 to 1.0×10−4 molL−1 with a detection limit of 8.0×10−8 molL−1 (defined as the concentration that could be detected at the signal-to-noise ratio of 3). The ECL sensor showed an outstanding well reproducibility and long-term stability. The established method has been applied to determine the glucose concentrations in real serum samples with satisfactory results. [Copyright &y& Elsevier]

Abstract: The electrochemiluminescent (ECL) behavior of lucigenin on a multi-wall carbon nanotube/nano-Au modified glassy carbon electrode (MWNT/nano-Au/GCE) was studied in this paper. Compared with the bare GCE, the ECL intensity of lucigenin can be greatly enhanced at MWNT/nano-Au/GCE. Based on the fact that superoxide dimutase (SOD) could obviously inhibit the ECL of lucigenin at MWNT/nano-Au/GCE, a sensitive ECL biosensor for determination of SOD was developed with a wide linear range of 5.0×10−8–5.0×10−6 mol/L with detection limit of 2.5×10−8 mol/L. [Copyright &y& Elsevier]

As a representative gas of food spoilage, the development of rapid hydrogen sulfide (H2S) analysis strategies for food safety control is in great demand. Despite traditional methods for H2S detection possessing great achievements, they are still incapable of meeting the requirement of portability and quantitative detection at the same time. Herein, a nanozyme catalysis pressure-powered sensing platform that enables visual quantification with the naked eye is proposed. In this methodology, Pt nanozyme inherits the catalase-like activity to facilitate the decomposition of H2O2 to O2, which can significantly improve the pressure in the closed container, further pushing the movement of indicator dye. Furthermore, H2S was found to effectively inhibit the catalytic activity of Pt nanozyme, indicating that the catalase-like activity of PtNPs may be regulated by varying concentrations of H2S. Therefore, by utilizing a self-designed pressure-powered microchannel device, the concentration of H2S was successfully converted into a distinct signal variation in distance. The effectiveness of the as-designed sensor in assessing the spoilage of red wine by H2S determination has been demonstrated. It exhibits a strong correlation between the change in dye distance and H2S concentration within the range of 1–250 μM, with a detection limit of 0.17 μM. This method is advantageous as it enhances the quantitative detection of H2S with the naked eye based on the portable pressure-powered sensing platform, as compared to traditional H2S biosensors. Such a pressure-powered distance variation platform would greatly broaden the application of H2S-based detection in food spoilage management. [ABSTRACT FROM AUTHOR]

A highly sensitive and selective electrochemiluminescence biosensor for detection of thrombin based on the strategy of target-induced conjunction of split aptamer fragments was developed. [ABSTRACT FROM AUTHOR]

T-2 toxin, a hazardous mycotoxin often present in cereals and products based on cereals, poses a substantial risk to humans and animals due to its high toxicity. The development of uncomplicated, quick and highly sensitive methods for detecting T-2 toxin is imperative. In this work, a portable sensing system was constructed using water column height as a readout device in combination with a controlled release system, which allows for an accurate quantitative analysis of T-2 toxin without the need for expensive instrumentation or skilled technicians. Hyaluronic acid (HA) hydrogel was constructed by double cross-linked DNA/aptamer hybrids with polyethyleneimine (PEI) and embedded with platinum nanoparticles (Pt NPs). The aptamer specifically bound to T-2 toxin in its presence, resulting in the disruption of the hydrogel and subsequent release of the Pt NPs. These Pt NPs were later mixed with a solution of H 2 O 2 in a confined reaction flask, leading to the decomposition of H 2 O 2 into O 2. A glass capillary tube containing a column of red water had been inserted into the cap of the reaction flask, and the low solubility of O 2 led to an increase in pressure within the reaction unit, causing the red water column to rise. There is a good linear correlation between the height of the capillary liquid level and the T-2 toxin concentration in the range of 20 ng/mL to 6 μg/mL. The system has been successfully used to detect T-2 toxin in samples of barley tea and corn. A portable biosensor for T-2 toxin quantification using water column height as readout based on target-responsive DNA hydrogel was developed. [Display omitted] • A portable, rapid and sensitive biosensor for T-2 toxin was developed. • The hydrogel cross-linked with DNA/aptamer shows high selectivity for T-2 toxin. • The biosensor used the height of capillary liquid level as readout, which can be measured with a ruler. • Target-responsive hydrogel was used for quantitative detection of T-2 toxin in real samples. [ABSTRACT FROM AUTHOR]

Circulating cell-free DNA (cfDNA) is known to be an attractive biomarker for liquid biopsy. In this work, a rapid and sensitive biosensor was achieved for cfDNA detection based on CRISPR-associated nuclease 12a (CRISPR-Cas12a) and single nanoparticle dark-field microscopy (DFM) imaging. The biosensor employed gold nanoparticles (AuNPs) as signal source, DFM as readout system, and Meanshift algorithms as the image processing systems, respectively. The presence or absence of cfDNA caused the different existing states (monomer or aggregated state) of AuNPs. AuNPs monomers could be effectively distinguished from the aggregated ones under DFM since the AuNPs aggregation could induced the green-to-yellow or green-to-red changing of scattering color. The monomer ratio easily obtained by Meanshift and partial least-square (PLS) algorithms was used for quantitative analysis. Using this strategy, breast cancer gene-1 (BRCA-1), a representative of cfDNA biomarker for breast cancer could be measured with high sensitivity in 40 min and has a low detection limit of 0.081 fM. It is hoped that this nucleic acid amplification-free sensor could be also utilized to detect other nucleic acid biomarkers, and thus, provides a novel strategy for biomedical image analysis. [Display omitted] • A new biosensor was developed for rapid and sensitive cfDNA detection. • This is a biosensing strategy avoiding nucleic acid amplification. • CRISPR-Cas12a and single nanoparticle DFM imaging had been applied to increase the sensitivity. • The Meanshift and partial least-square (PLS) algorithms was used for quantitative analysis. • This biosensor had been used to detect the breast cancer gene-1 (BRCA-1) in cell lysates with satisfied performance. [ABSTRACT FROM AUTHOR]

Herein, magnetic electrochemiluminescence (ECL) nanoparticle Fe 3 O 4 @PtPd/Ru(bpy) 3 2+ had been synthesized then been coupled with CRISPR/Cas13a system and Zn2+ dependent DNAzyme to design a novel ECL biosensor for specific detection of microRNA-145 (miRNA). The synthesized multifunctional magnetic nanoluminescent materials Fe 3 O 4 @PtPd/Ru(bpy) 3 2+ not only load Ru(bpy) 3 2+ to provide ECL signals, but also can quickly achieve separation and enrichment from complex matrices. In addition, ferrocene (Fc) was used as a quencher in the Ru(bpy) 3 2+/tripropylamine (TPA) system. Fc was modified on DNA bound to Fe 3 O 4 @PtPd. Benefited from the highly specific recognition ability of CRISPR/Cas13a, the target miRNA induces CRISPR/Cas13a trans -cleavage to trigger the Zn2+-dependent DNAzyme cyclic cleavage to realize the dual signal amplification. DNA modified by Fc was split by target miRNA-induced cleaving, and then magnetic separation was performed to keep Fc away from the surface of the nanoparticles. Thus, the enhanced ECL signal was obtained to detect miRNA-145. Under optimized conditions, the prepared sensor showed a wide linear range (1 fM to 1 nM) and a low limit of detection (LOD) down to 0.41 fM. Furthermore, it shows excellent selectivity and good reproducibility. The proposed ECL platform has huge potential applications in the development of various sensitive sensors for detecting the other miRNA. Magnetic electrochemiluminescence (ECL) nanoparticle Fe 3 O 4 @PtPd/Ru(bpy) 3 2+ had been synthesized then been coupled with CRISPR/Cas13a system and Zn2+ dependent DNAzyme to design a novel ECL biosensor for specific detection of microRNA-145. [Display omitted] • A ECL biosensor based on specific recognition ability of CRISPR/Cas13a was developed. • Multifunctional magnetic nanoluminescent materials Fe 3 O 4 @PtPd/Ru was synthesized. • Dual signal amplification was achieved by combining CRISPR/Cas13a system and DNAzyme. • The ECL biosensor exhibited a lower detection limit and a wider detection range. [ABSTRACT FROM AUTHOR]

A colorimetric and photothermal dual readout biosensor for Flap endonuclease 1 (FEN1) quantification was developed on the basis of target-prevented gold nanoparticles (AuNPs) aggregation. The exposed 5′-flap of double-flap DNA substrate modified on SAMBs was firstly cleaved by FEN1. Large amount of cleaved 5′-flap remained in the supernatant after simple magnetic separation, which can adsorb on the surface of AuNPs and effectively prevent the dispersed AuNPs from aggregation under high ionic concentration, accompanied with the color changing of the system, which can be recognized by nake eyes easily. The absorption intensity at 528 nm shows a good linear relationship with the increasing FEN1 concentration from 5.0 × 10-3 to 3.1 × 10-2 U μL-1 with a LOD of 1.6 × 10-3 U μL-1 (S/N = 3). Given the aggregated AuNPs have higher photothermal effect than that of the dispersed AuNPs, the target-prevented AuNPs aggregation avoids a sharp increase of temperature for the system under the laser radiation. The temperature change is linearly correlated with the FEN1 concentration in the range of 3.1 × 10-3–6.1 × 10-2 U μL-1 with a LOD of 1.1 × 10-3 U μL-1. The whole detection process can be completed within 1 h. The proposed system had been applied to detect FEN1 concentration in serum samples with satisfied results, which can be applied in resource-limited area easily and quickly. A colorimetric and photothermal dual readout biosensor for Flap endonuclease 1 (FEN1) quantification was developed on the basis of target-prevented gold nanoparticles (AuNPs) aggregation. [Display omitted] • A photothermal and colorimetric dual modes biosensor was developed for FEN1 detection. • Naked eyes or common thermometer had been used readout. • The concentration of FEN1 can be detected in less than 1 h. • This biosensor had been used to evaluate the targets in serum samples. [ABSTRACT FROM AUTHOR]

Graphical abstract An electrically heated indium-tin-oxide electrode was employed for in situ temperature control during the process of DNA hybridization and target recognition. The capability in temperature control was similar to bulk similar heating, but the performance was superior. Highlights • DNAzyme-based electrochemiluminescence biosensor was used for the sensitive monitor of Pb2+. • Heated Indium-tin-oxide (ITO) electrode was employed as the in situ temperature controller. • Better performance was achieved by using Y-shaped DNA and heated ITO electrode. Abstract The temperature control in the traditional DNAzyme-based electrochemiluminescent (ECL) biosensors for Pb2+ is realized through bulk solution heating, which needs tedious procedures, relative large equipment and this limits their application. Moreover, the ECL indicators had been modified on the DNA through chemical reaction, which has the limitation of low efficiency and high cost. In this study, electrically heated indium-tin-oxide (ITO) electrode is applied to adjust the temperature instead of the whole bulk solution heating. Y-shaped double strand DNA (dsDNA) was formed through the hybridization of DNAzyme, substrate and capture DNA, then Ru(phen) 3 2+ was embedded into the groove of dsDNA and acted as the ECL indicator, which avoided the costly labeling procedure of ECL indicator on DNA. The results indicated that the two different ways of heating had the same effects on the DNA hybridization and DNAzyme action, but the temperature controlled by the heated electrode is simpler and quicker than that with bulk solution heating. Furthermore, the performance of the biosensor had been further improved at an elevated electrode surface temperature because temperature affected the performance of the ECL of Ru(phen) 3 2+ greatly. Under the optimized conditions, the ECL signal has a linear relationship with logarithm concentration of Pb2+ in the range of 0.25 ˜ 500 pM with a detection limit of 0.2 pM at the electrode temperature of 45 °C, and this outcome was approximately 5 times lower than that at 25 °C of electrode surface temperature. The proposed biosensor has been applied to detect Pb2+ in soil samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Highlights • Cu2+-C 3 N 4 /AuNBPs based multicolor NSE sensor is fabricated for the first time. • The vivid color changes are generated by NSE induced etching of Au NBPs. • Cu2+-C 3 N 4 /AuNBPs based naked eye detection of NSE in human serum is demonstrated with a LOD of 92.8 pM. Abstract In this work, we have synthesized Cu2+-modified carbon nitride nanosheets (Cu2+-C 3 N 4) as peroxidase mimic catalytic substance, which is more active than the horseradish peroxidase enzyme in extreme environments. Gold nanobipyramid (Au NBP) is a good chromogenic substrate for multicolor display because the longitudinal plasmon bands of AuNRs can be easily tuned by adjusting their aspect ratios and used as an excellent indicator for colorimetric detection of immunoassays. The generation of TMB2+ from sandwich complex (peroxidase-like catalysis) efficiently etches Au NPBs to produce multicolor variations from brown to olive, green, blue, purple, purple, red, pink, and colorless in presence of varied concentrations of neuron specific enolase (NSE). The experimental results show that the colorimetric detection ranging from 312.5 to 20,000 pM with a detection limit of 92.8 pM, which is higher than other multicolor based sensors. The Cu2+-C 3 N 4 nanosheets and Au NBPs based colorimetric visual (naked eye) semi-quantitative method as a potential platform towards the detection of important biomolecules in clinical and therapeutic applications. The proposed method is simple, low-cost and enzyme-free to detect NSE for the first time. [ABSTRACT FROM AUTHOR]

Highlights • An ECL biosensor for hyaluronidase detection based on the electrostatic interaction was developed for the first time. • The developed sensor was also used to detect HAase inhibitor with high efficiency. • The limit of detection for hyaluronidase was 0.33 U/mL. Abstract The development of simple and sensitive method for hyaluronidase (HAase) detection is significant for the clinical diagnosis and treatment of cancer as HAase is a potential tumor marker. In this study, a simple but sensitive electrochemiluminescence (ECL) biosensor has been designed for HAase detection based on the electrostatic interaction of anionic hyaluronic acid (HA) and cationic luminous reagent Ru(bpy) 3 2+. Ru(bpy) 3 2+ is adsorbed on HA through electrostatic interaction to form HA-Ru(bpy) 3 2+ complex. The Ru(bpy) 3 2+ in the HA-Ru(bpy) 3 2+ complex cannot be filtered out because of its large molecular weight. In the presence of HAase, the HA in HA-Ru(bpy) 3 2+ can be cleaved into fragments by enzymatic hydrolysis. As a result, the Ru(bpy) 3 2+ attached on the HA fragments can be separated from the HA-Ru(bpy) 3 2+ complex by centrifugation easily. The resulting ultrafiltrate containing Ru(bpy) 3 2+ can be used to characterize the concentration of HAase in the sample. The ECL intensity of Ru(bpy) 3 2+ has a linear relationship with the concentration of HAase in the range of 2.0–40 U/mL with a detection limit of 0.33 U/mL. The proposed ECL system has been applied to detect HAase in urine samples with satisfied results and HAase inhibitor with high efficiency. [ABSTRACT FROM AUTHOR]

Bacterial infection of wounds is one of great concern to patients, and rapid and correct detection of bacterial infection is crucial to ensure accurate diagnosis and early intervention. Based on the principle that glucose can only be consumed by live bacteria, a fluorescent biosensor was constructed to detect four kinds of common infectious bacteria (Acinetobacter baumannii, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus) in skin wounds, taking advantage of magnetic bead-aptamer for recognizing, sorting and enrichment, platinum nanoparticles for signal amplification. The linear detection range of AB, EC, PA and SA were 27– 8 × 106 CFU/mL, 10– 2.5 × 107 CFU/mL, 34– 2.5 × 107 CFU/mL and 10– 1.0 × 107 CFU/mL, respectively, and the limits of detection were 27 CFU/mL, 10 CFU/mL, 34 CFU/mL and 2 CFU/mL. Furthermore, all target bacteria in samples containing 8 × 108 CFU/mL of other interfering bacteria have been successfully identified and quantified. The proposed method was also successfully applied to the detection of bacterial infection in skin wounds of mouse and human, including the detection of separate bacterial infection as well as a coinfection. The recovery of this method was in the range of 90.161– 109.961%. Thus, this proposed method can be a promising candidate for rapid and convenient evaluation of infectious bacteria in point-of-care settings. • Established a fluorescence detection sensor for four types of wound infection bacteria. • This sensor utilizes magnetic beads-aptamer to isolate four types of infectious bacteria. • Quantification of four infectious bacteria based on glucose oxidase reaction. • The biosensor detected wound infection bacteria as low as 10 CFU/mL. [ABSTRACT FROM AUTHOR]

The amino-functionalized metal organic framework (NH 2 -Cu-MOF) was fabricated via bottom-up synthesis strategy. Detailed characterization using electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy demonstrated that the as-synthesized NH 2 -Cu-MOF was two-dimensional nanosheet (a thin thickness ∼4.2 nm). Results showed that the as-synthesized NH 2 -Cu-MOF nanosheet possessed fluorescence property (λ em  = 425 nm) as well as peroxidase mimic activity. On the basis of these two properties, we proposed a biosensor for hypoxanthine detection. The fluorescence intensity had a linear relationship with the hypoxanthine concentration in the range of 10–2000 μM. The limit of detection was 3.93 μM (S/N = 3). This work contributes to the synthesis of a new two-dimensional MOF nanosheet and extends the application of two-dimensional MOF nanosheet on biological luminescent sensors. [ABSTRACT FROM AUTHOR]

The difference of electrostatic interaction between free Ru(phen) 3 2+ and Ru(phen) 3 2+ embedded in double strand DNA (dsDNA) to the negatively charged indium tin oxide (ITO) electrode has been applied to develop a homogeneous and label-free electrochemiluminescence (ECL) aptasensor for the first time. Ochratoxin A (OTA) has been chosen as the model target. The OTA aptamer is first hybridized with its complementary single strand DNA (ssDNA) to form dsDNA and then interacted with Ru(phen) 3 2+ via the grooves binding mode to form dsDNA-Ru(phen) 3 2+ complex, which remains negatively charged feature as well as low diffusion capacity to the negatively charged ITO electrode surface owing to the electrostatic repulsion. Meanwhile, the intercalated Ru(phen) 3 2+ in the grooves of dsDNA works as an ECL signal reporter instead of the labor-intensive labeling steps and can generate much more ECL signal than that from the labeling probe. In the presence of target, the aptamer prefers to form an aptamer-target complex in lieu of dsDNA, which induces the releasing of Ru(phen) 3 2+ from the dsDNA-Ru(phen) 3 2+ complex into the solution. With the assistance of RecJ f exonuclease (a ssDNA specific exonuclease), the released ssDNA and the aptamer in the target-complex were digested into mononucleotides. In the meantime, the target can be also liberated from OTA-aptamer complex and induce target cycling and large amount of free Ru(phen) 3 2+ present in the solution. Since Ru(phen) 3 2+ contains positive charges, which can diffuses easily to the ITO electrode surface because of electrostatic attraction, causing an obviously enhanced ECL signal detected. Under the optimal conditions, the enhanced ECL of the system has a linear relationship with the OTA concentration in the range of 0.01–1.0 ng/mL with a detection limit of 2 pg/mL. This innovative system not only expands the immobilization-free sensors in the electrochemiluminescent fields, but also can be developed for the detection of different targets easily with the same strategy by changing the aptamer used. [ABSTRACT FROM AUTHOR]

A promising and novel electrochemiluminescence (ECL) aptasensor equipped with an electrically heated indium tin oxide (ITO) electrode was constructed. Temperature control was achieved by heating the ITO electrode, avoiding the tedious operation and substantial increase in noise experienced when heating the bulk solution. Using the heated ITO electrode, an order of magnitude improvement in ECL sensitivity was obtained by operating the electrode at 65 °C compared to 25 °C, and this can be used to further enhance the performance of the biosensor. [ABSTRACT FROM AUTHOR]

In most aptamer based stimulus response mesoporous silica nanoparticles (MSN) systems, the aptamer is modified on the MSN via electrostatic interaction, however leakage might exist after a certain time in the system and hence the stability is not good. In this study, the pores of MSN were capped by aptamer through click chemistry reaction for the first time and the system was then employed to develop a fluorescence biosensor. Specifically, the aptamer of the target (thrombin in this study) was hybridized with its complementary DNA (which was initially modified with alkyne at the terminal) to form a double strand DNA (dsDNA) firstly, and then this dsDNA was modified on N 3 modified MSN via Cu(I) catalyzed alkyne-azide cycloaddition reaction. The guest molecules (fluorescein) were blocked in the pores of the MSN with high efficiency and nearly no leakage was detected. Upon the introduction of thrombin, thrombin specifically recognized its aptamer, so aptamer released from the MSN; and the single strand DNA(ssDNA) left could not cap the pores of the MSN efficiently and hence caused the releasing of fluorescein into the solution. The enhanced fluorescence intensity of the system has a good linear relationship with the thrombin concentration in the range of 50–1000 ng mL −1 with a detection limit of 28.46 ng mL −1 . The proposed biosensor has been successfully applied to detect thrombin in serum samples with high selectivity. The same strategy can be applied to develop biosensors for different targets by changing the adopted aptamer. [ABSTRACT FROM AUTHOR]

Fish product is one of the main seafood with the disadvantage of easy to perish. Various indexes and diverse methods have been developed to evaluate the fish freshness, but most of them are complex and cannot be applied for on-field detection. In this study, we reported a simple, visual and economical multicolor biosensor based on the etching of gold nanorods (GNRs) to evaluate the fish freshness with the naked eye. Hypoxanthine (Hx) is chosen as the index of fish freshness and it react with the dissolved oxygen to produce H 2 O 2 at the presence of xanthine oxidase (XOD). Then GNRs are etched quickly by the H 2 O 2 in the presence of Fe 2+ . Correspondingly, the GNRs surface plasmon resonance (SPR) is regulated and results in a distinctly color change of the system, which can be easily distinguished with the naked eye. Therefore, the concentration of Hx in the fish samples can be semi-quantitatively analyzed with the naked eye. The proposed multicolor Hx sensor has been successfully applied to the detection of Hx in fish samples. [ABSTRACT FROM AUTHOR]

Hyaluronidase (HAase) is a potential tumor biomarker for diseases of the digestive tract and nervous system, the development of simple and sensitive techniques for HAase determination is urgent needed. Gold nanorods (Au NRs) can be etched by H 2 O 2 with high efficiency and display color changing. In this work, a HAase-responsive hydrogel system had been designed and the amount of H 2 O 2 spilled from the system had a close relationship with the amount of HAase, then the spilled H 2 O 2 had been applied to etch Au NRs. The color change of the solution was used to realize semi-quantitative determination of HAase. Furthermore, the longitudinal peak shift of Au NRs had a linear correlation with the concentration of HAase in the range of 10–60 U/mL (within 40 min) and the limit of detection (LOD) was 3.8 U/mL (S/N = 3), which can be used to realize accurate quantitative analysis of HAase. The proposed method has been applied to monitor HAase in serum of pancreatic cancer patients with satisfied results. • A rapid response and sensitive multicolor biosensor for HAase was developed. • The hydrogel encapsulated with Pt NPs has high selectivity toward HAase. • Au NRs etched by ROS triggered the change of the UV absorption peak which could be used to accurately detection of HAase. • Rapid on-site detection of HAase by naked eyes can be achieved by observing the color change of Au NRs solution. [ABSTRACT FROM AUTHOR]

Development of simple but sensitive biosensor for influenza detection is highly important in immediate and effective clinical treatment. In this study, a sensitive colorimetric immunosensor which combines the advantages of high selectivity of immunoassay and simplicity of colorimetric detection has been developed to detect influenza virus H5N1 based on enzyme-encapsulated liposome. Biotin-tagged liposome encapsulated with large amount of horseradish peroxidase (HRP) was firstly synthesized. In the presence of H5N1, H5N1 co-bound with the capture antibody and the biotinylated detection antibody to form sandwich immunocomplex. Subsequently, the HRP-encapsulated liposome was introduced to conjugate with the detection antibody through biotin-avidin-biotin linkage. Upon the addition of substrate (mixture of 3,3′,5,5′-tetramethylbenzidine (TMB) and H 2 O 2 ), the liposome was directly lysed to release large amount of HRP by TMB. The released HRP catalyzed the H 2 O 2 -mediated oxidation of TMB, resulting in color change of the system, which was observed by naked eyes or UV–vis spectra. The result showed that the absorption intensity enhanced with the increase of H5N1 concentration ranging from 0.1 to 4.0 ng/mL, and the detection limit was calculated to be 0.04 ng/mL. The sensitivity of the proposed biosensor is much higher than that of conventional enzyme-linked immunosorbent assay method. The proposed immunosensor is relatively simple, low-cost, sensitive, and selective without using any sophisticated instruments, therefore it may have a promising prospect for detecting targets in clinical medicine, food safety analysis, and environmental monitoring. [ABSTRACT FROM AUTHOR]

Severe acute respiratory syndrome coronavirus (SARS-CoV-2) is rampant all over the world, and rapid and effective virus detection is the best auxiliary to curb the spread of the epidemic. A diagnosis can only be made if two or more different nucleic acid sequences are confirmed at the same time, and in most of traditional detection technologies, these target sequences have been detected separately. In this work, an electrochemiluminescent (ECL) biosensor employing a single ECL probe as signal output and responding to dual-target simultaneously is proposed for the first time. Taking the two sequences located in ORF 1ab region and N region of SARS-CoV-2 gene sequence as the model target and nitrogen doped carbon quantum dots (CDs) as ECL beacon, supplemented with catalytic hairpin assembly (CHA) reaction for signal amplification, the presented strategy has been successfully applied to the rapid detection of SARS-CoV-2. The developed SARS-CoV-2 biosensor based on the series CHA systems can realize the quantitative determination of SARS-CoV-2 in the range of 50 fM to 200 pM within 40 min. Moreover, the clinical validity of this method has been verified by the high consistency between the detection results of using this method and those using RT-qPCR for seven clinical pharyngeal swab samples. • A dual-target DNA sequences response ECL biosensor had been developed. • Two sequences located in ORF 1ab region and N region of SARS-CoV-2 gene sequence had been chosen as the model target. • Series catalytic hairpin assembly amplification had been used to realize signal amplification. • Nitrogen doped carbon quantum dots (CDs) had been used as ECL probe. [ABSTRACT FROM AUTHOR]

• A homogeneous ECL biosensor was developed for microRNA-155 detection. • Enzyme-free cascade amplification strategy was composed of CHA and HCR. • Magnetic enrichment technique could reduce background signal and enrich target. MicroRNA-155 (miR-155) can act as a suitable biomarker for dry eye diseases caused by Sjögren's syndrome. Since the concentration of miR-155 in the clinic samples is low, it is necessary to develop some simple but sensitive detection methods. In this study, a homogeneous electrochemiluminescence (ECL) biosensor for miR-155 detection based on catalyze hairpin assembly (CHA) and hybridization chain reaction (HCR) and magnetic assisted enrichment had been constructed. Firstly, biotin-modified hairpin H1 (bio-H1) had been connected with the streptavidin-modified magnetic beads (SAMBs) to capture target, which can be used to trigger CHA reaction to complete the first signal amplification with the assistance of hairpin H2. Then the stick end of H2 of the CHA production can trigger the HCR reaction of H3 and H4 and generate long double-stranded DNAs (dsDNAs) on the surface of SAMBs to realize the second signal amplification. Ru(phen) 3 2+ can insert into the dsDNAs to produce SAMBs/dsDNA/Ru and act as signal tags, which can be purified by magnetic separation easily, making the background signal significantly reduced. The ECL intensity of the system had a linear relationship with logarithm of miR-155 concentration in the range of 1 fM ∼ 10 nM, with a detection limit as low as 0.63 fM. The proposed biosensor had been applied to monitor miR-155 in clinical samples with satisfied results. [ABSTRACT FROM AUTHOR]

The electrostatic attraction difference between negatively charged report probes and positively charged electrode had been applied to develop a signal-on low background electrochemiluminescence (ECL) biosensor for microRNA-141 (miRNA141, chosen as a model target) detection. Indium tin oxide (ITO) electrode was modified with poly-(allylamine hydrochloride) (PAH) to generate a positively charged surface. The electrostatic repulsion between dichlorotris (1,10-phenanthroline) ruthenium (Ⅱ) hydrate (Ru(phen) 3 2+) and ITO electrode results in the low background signal. The target can trigger an enzyme-free isothermal catalytic hairpin self-assembly (CHA) and hybrid chain reaction (HCR) cascade reaction to generate a large amount of negatively charged long dsDNAs, which can be used to load Ru(phen) 3 2+ (Ru-dsDNA) with high efficiency. Ru-dsDNA complexes are negatively charged and can easily accumulate on ITO electrode surface because of electrostatic attraction, which results in a strong ECL signal detected. The ECL intensity of the system was linearly correlated with the logarithm of microRNA-141 concentration in the range of 1 fM ∼ 5 pM with a detection limit of 0.17 fM (S/N = 3). The reliability of the proposed biosensor had been verified through the detection of targets in cell lysates. • A homogeneous electrochemiluminescence (ECL) biosensor was designed for microRNA-141 detection. • Homogeneous strategy avoiding the tedious and cumbersome electrode surface modification process. • Enzyme-free isothermal amplification of CHA and HCR was used to achieve target recovery and efficient signal amplification. • The electrostatic attraction between Ru-dsDNA and PAH-modified ITO electrode effectively reduced the background signal. • This biosensor had been used to evaluate the targets in cell lysates with satisfied performance. [ABSTRACT FROM AUTHOR]

Alkaline phosphatase (ALP) plays an important role in phosphate metabolism processes; deviation from its normal level may indicate different kinds of diseases, so it is highly necessary to develop some simple and sensitive methods to monitor the ALP level. In this study, a simple, high selective, and sensitive fluorescent biosensor has been proposed for ALP activity determination. The Cu(II)-dependent DNAzyme (Cu-Enzyme) are divided into two parts: Cu-Enzyme 1 and Cu-Enzyme 2, and labelled with alkyne and azido groups, respectively. The Cu-substrate (Cu-Sub) is labelled with a FAM fluorophore (6-carboxyfluorescein) at the 3′-end and an additional quencher (BHQ1) at the 5′-end. The 5′-end of Cu-Enzyme 1 is labelled with BHQ1 as well. The hybridization of the Cu-Enzyme 1 and Cu-Enzyme 2 with Cu-Sub strand results in the low background fluorescence signal because the fluorescence from FAM is quenched. The addition of ALP can hydrolyze AA-P into AA, which can reduce Cu(II) into Cu(I) and in turn catalyze the cycloaddition of Cu-Enzyme 1 and Cu-Enzyme 2 to form a modified Cu-Enzyme. Then the modified Cu-Enzyme catalyzes the cleavage of the Cu-Sub strands into two pieces. One piece containing FAM fluorophore can easily diffuse into solution and give off a strong fluorescence signal. The enhanced fluorescent intensity has a linear relationship with the ALP concentration in the range of 0.36–54.55 U L −1 with the detection limit of 0.14 U L −1 (S/N = 3). The proposed biosensor has been successfully applied to detect ALP in serum samples with satisfied results. [ABSTRACT FROM AUTHOR]

The determination of folate receptor (FR) that over expressed in vast quantity of cancerous cells frequently is significant for the clinical diagnosis and treatment of cancers. Many DNA-based electrochemical biosensors have been developed for FR detection with high selectivity and sensitivity, but most of them need complicated immobilization of DNA on the electrode surface firstly, which is tedious and therefore results in the poor reproducibility. In this study, a simple, sensitive, and selective electrochemical FR biosensor in cancer cells has been proposed, which combines the advantages of the convenient immobilization-free homogeneous indium tin oxide (ITO)-based electrochemical detection strategy and the high selectivity of the terminal protection of small molecule linked DNA. The small molecule of folic acid (FA) and an electroactive molecule of ferrocence (Fc) were tethered to 3′- and 5′-end of an arbitrary single-stranded DNA (ssDNA), respectively, forming the FA-ssDNA-Fc complex. In the absence of the target FR, the FA-ssDNA-Fc was degraded by exonuclease I (Exo I) from 3′-end and produced a free Fc, diffusing freely to the ITO electrode surface and resulting in strong electrochemical signal. When the target FR was present, the FA-ssDNA-Fc was bound to FR through specific interaction with FA anchored at the 3′-end, effectively protecting the ssDNA strand from hydrolysis by Exo I. The FR-FA-ssDNA-Fc could not diffuse easily to the negatively charged ITO electrode surface due to the electrostatic repulsion between the DNA strand and the negatively charged ITO electrode, so electrochemical signal reduced. The decreased electrochemical signal has a linear relationship with the logarithm of FR concentration in range of 10 fM to 10 nM with a detection limit of 3.8 fM (S/N=3). The proposed biosensor has been applied to detect FR in HeLa cancer cells, and the decreased electrochemical signal has a linear relationship with the logarithm of cell concentration ranging from 100–10000 cell/mL. Compared with the traditional heterogeneous electrochemical FR biosensors, the proposed biosensor owns the merits of the simplicity and high specificity, presenting the great potential application in the area of early diagnosis of cancers. [ABSTRACT FROM AUTHOR]

The lack of large-scale human papillomavirus (HPV) DNA screening is a major contributor to the high incidence and mortality of cervical cancer in economically undeveloped areas. The development of sensitive, rapid, and low-cost screening techniques is urgently needed. Here, DNA nanoflowers encapsulating glucose oxidase and horseradish peroxidase (GHDFs) were synthesized by one-pot rolling circle amplification, and then the GHDFs were used as the cargo of DNA hydrogel and applied for HPV DNA detection. When target DNA was present, the DNA hydrogel cross-linking structure was disrupted, releasing GHDFs, which then catalysed the oxidation of glucose and tetramethylbenzidine in a cascade, generating a significant electrical signal. Signal intensity had a linear relationship with the logarithm of target DNA concentration in the range of 10 fM-1 nM with a detection limit of 3.76 fM. The detection time of the proposed biosensor was 25 min, which was suitable for large-scale HPV DNA screening in economically underdeveloped areas and provides a blueprint for the detection of other DNA of interest. • An electrochemical biosensor for HPV screening had been developed. • DNA nanoflowers encapsulating two enzymes had been applied. • Cascade catalyzed amplification strategy was fully exploited. • The biosensor detection time required only 25 min, detection limit was 3.76 fM. [ABSTRACT FROM AUTHOR]

Mesoporous silica nanoparticles (MSN) based controlled release system had been coupled with diverse detection technologies to establish biosensors for different targets. Chemiluminescence (CL) system of luminol/H 2 O 2 owns the characters of simplicity, low cost and high sensitivity, but the targets of which are mostly focused on some oxidants or which can participate in a chemical reaction that yields a product with a role in the CL reaction. In this study, chemiluminescent detection technique had been coupled with mesoporous silica-based controlled released system for the first time to develop a sensitive biosensor for the target which does not cause effect to the CL system itself. Cocaine had been chosen a model target, the MSN support was firstly loaded with glucose, then the positively charged MSN interacted with negatively charged oligonucleotides (the aptamer cocaine) to close the mesopores of MSN. At the present of target, cocaine binds with its aptamer with high affinity; the flexible linear aptamer structured will become stems structured through currently well-defined non-Waston–Crick interactions and causes the releasing of entrapped glucose into the solution. With the assistant of glucose oxidase (GOx), the released glucose can react with the dissolved oxgen to produce gluconic acid and H 2 O 2 , the latter can enhance the CL of luminol in the NaOH solution. The enhanced CL intensity has a relationship with the cocaine concentration in the range of 5.0–60 μM with the detection limit of 1.43 μM. The proposed method had been successfully applied to detect cocaine in serum samples with high selectivity. The same strategy can be applied to develop biosensors for different targets. [ABSTRACT FROM AUTHOR]

An ultrasensitive homogeneous electrochemiluminescence biosensor for FEN1 detection had been developed on the basis of branched hybridization chain reaction (BHCR) amplification and ultrafiltration technology. [Display omitted] • An ultrasensitive ECL biosensor for FEN1 detection had been proposed. • Homogeneous strategy avoids tedious and cumbersome electrode modification. • Branched hybridization chain reaction was applied to increase the sensitivity. • The biosensor can be used to evaluate FEN1 activity in cells and serum samples. A sensitive homogeneous electrochemiluminescence (ECL) biosensor for flap endonuclease 1 (FEN1) detection was developed by combining highly sensitive ECL detection, high efficiency of branched hybridization chain reaction (BHCR) amplification, a convenient homogeneous strategy, and simple ultrafiltration separation. Magnetic beads were first modified with well-designed double flap DNAs containing 5′-flaps. In the presence of FEN1, the 5′-flap can be cleaved, and a large amount of single-stranded DNA can be produced, which can be separated easily from the double-flap DNA-modified beads by a magnet. Then, the cleaved 5′-flap can be used to initiate BHCR amplification to produce a large amount of long-strand dsDNA. Ru(phen) 3 2+ can insert dsDNA to form Ru-dsDNAs, which can be easily separated from the main solution through ultrafiltration. The ECL signal from the separated Ru-dsDNAs has a good linear relationship with the logarithm of the FEN1 concentration ranging from 6.5 × 10−2 ∼ 6.5 × 103 U/L with a detection limit of 2.2 × 10−2 U/L. The proposed biosensor was used to evaluate FEN1 activity in real samples with satisfactory results. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemiluminescence biosensor for HPV16 detection had been developed. • The sensor are based on the steric hindrance effect of Au nanocages. • Exonuclease III assisted amplification strategy had been applied to realize sensitive detection. • The enhanced ECL signal had a relationship with HPV16 DNA concentration in the range of 10 fM to 100 pM. The effect of steric hindrance of electrode surface can affect the diffusion of the Ru(bpy) 3 2+ toward electrode and thus in turn affect the ECL performance of the system. In this study, this character had been adopted to develop a biosensor for HPV DNA detection. Exonuclease III (Exo III) signal amplification strategy had been applied to realize signal amplification. First, hairpin probes (HP) was anchored on the surface of electrode as capture probes, HP can resistant to the hydrolyzation of Exo III due to its 3′-protruding termini. Without the target, a large amount of cDNA modified Au nanocages (AuNCs-cDNA) can hybridize with HP and connected to surface of electrode, weak ECL signals can be detected since Ru(bpy) 3 2+ can not diffuse freely to the electrode surface because of the steric hindrance of AuNCs-cDNA. In the presence of the target, HP can hybridize with the target to form double-stranded DNA (dsDNA) with a blunt 3′ terminus, due to the high preference of Exo III for cleaving dsDNA with a blunt 3′ termini, HP in dsDNA was hydrolyzed, and the target which formed dsDNA was released to hybridize with another HP, inducing the Exo III assisted amplification strategy. Due to the reduction of HP on electrode surface, the amount of AuNCs-cDNA connected to the electrode surface become small, a high ECL signal can be detected. Under the optimal conditions, the ECL response of the system has a linear relationship with logarithm of target DNA concentration in the range of 10 fM to 100 pM, and a detection limit of 3.54 fM (S/N = 3). The proposed biosensor has high sensitivity and selectivity, which had been applied to the detection of target DNA in real sample and the satisfied results had been obtained. This system also can detect different targets by changing the DNA sequence easily. [ABSTRACT FROM AUTHOR]

Determination of ochratoxin A (OTA) is highly important for food safety control. In this study, a signal-on electrochemiluminescence (ECL) biosensor which combined the characteristics of high efficiency of hyperbranched rolling circle amplification (HRCA) and high selectivity of aptamer was developed for OTA determination. The capture probe DNA (CDNA) was firstly immobilized on the gold electrode surface through Au–S interaction, then the OTA aptamer was modified on the electrode surface through hybridization with CDNA. Since OTA can competitively bind with the aptamer due to their high affinity, which would induce the releasing of aptamer from the electrode surface. Subsequently, the free CDNA on the electrode surface can hybridize with the padlock probe and induce HRCA reaction subsequently. Thus, the HRCA products which contained large amount of double-stranded DNA (dsDNA) fragments can be accumulated on the electrode surface. Since Ru ( phen ) 3 2 + can intercalate into the groove of dsDNA and acts as ECL indicator, high ECL intensity can be detected from the electrode surface. The enhanced ECL intensity has a linear relationship with OTA in the range of 0.05–500 pg/mL with a correlation coefficient of 0.9957, and the limit of detection (LOD) was 0.02 pg/mL. The developed biosensor has been applied to determine OTA concentration in the corn samples with satisfied results. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemiluminescence (ECL) aptamer sensor for protein (thrombin as an example) detection based on hyperbranched rolling circle amplification (HRCA) had been developed. A complementary single-strand DNA (CDNA) of the thrombin aptamer had been modified on the gold electrode firstly, and then hybridized with thrombin aptamer to make the aptamer immobilized on the electrode surface, in the presence of thrombin, aptamer–thrombin bioaffinity complexes formed and made thrombin aptamer leave the electrode surface. Thus, the linear padlock probe hybridized with the free CDNA on the electrode surface and circularized by Escherichia coli DNA ligase. Subsequently, the linear padlock probe was served as a template for the initiation of HRCA reaction, and a lot of dsDNA modified on the electrode surface. Then Ru(phen) 3 2+ (acted as the ECL indicator) intercalates specifically into double-stranded DNA (dsDNA) grooves to generate ECL signal. The ECL intensity of the system has a linear relationship with thrombin concentration in the range of 3.0–300 aM with a detection limit of 1.2 aM ( S / N =3). The proposed method combines the high sensitivity of ECL, exponential amplification of HRCA for signal enhancement and high selectivity of aptamer. [ABSTRACT FROM AUTHOR]