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Abstract: A novel biosensor for the detection of thrombin was developed by using QDs electrochemiluminescence (ECL) technique. The thiol-terminated aptamer with 15 nucleotides (probe I) was first immobilized on Au electrode, and then thrombin was imported to form the aptamer–thrombin bioaffinity complexes. Another 5′-biotin modified aptamer (29 nucleotides, probe II) was next hybridized with the combined thrombin to form a sandwich type structure. Streptavidin modified QDs (avidin–QDs) were bound to probe II via the biotin–avidin-system. The QDs ECL signal was responsive to the amount of probe II, which was indirect proportional to the combined thrombin. The ECL intensity of the biosensor increased with the increase of thrombin concentration in the range of 0–20μgmL−1. In addition, the biosensor exhibited the excellent selectivity responses and good stability toward the target analyte. [Copyright &y& Elsevier]

Abstract Along with the advance in medical research, more biomarkers emerge as useful indicators for both disease and health index. However, majority of them have no practical or economic testing methods available yet, or rely on high-costing methods such as Enzyme-Linked Immuno-Sorbent Assay (ELISA), High-Performance Liquid Chromatography (HPLC), Mass Spectrum, and immunohistochemistry (IHC). In this article, we develop a universal nanozyme integrated testing platform for biological molecules that incorporates the electrochemical measurement of glucose with lateral flow immunostrip (LFS) for target analytes. This design involves the quantitative conversion of analytes into invertase and then glucose, which can be measured by an extremely affordable meter. The feasibility of this design was validated using 8-hydroxy-2'-deoxyguanosine (8-OHdG) and prostate specific antigen (PSA) as representatives for small molecules and moderate to large proteins respectively. Our approach yields results comparable to commercial diagnostic ELISA kits at a substantially reduced cost and reaction time. Specifically, the design has a detection limit of 0.23 ng mL-1 for 8-OHdG and 1.26 ng mL-1 for PSA, and a detection range of 0.1–100 ng mL-1 for 8-OHdG and 1–100 ng mL-1 for PSA. By combining the accessibility of well-established glucose testing and LFS, our design can serve as a point of care testing method that can be fully integrated into the personal lifestyle without requiring professional assistance. Highlights • Developed a universal nanozyme integrated lateral fluidic sensing platform. • Non-glucose biomarkers can be measured by a glucose meter based on this platform. • Two types of molecules were successfully detected through this platform. • The sensor was easy to fabricate and convenient to operate. • This approach will provide new opportunities for the detection of other targets. [ABSTRACT FROM AUTHOR]

The accurate therapeutic evaluation for chronic myeloid leukemia (CML) drug is of great importance to minimize side effects and enhance efficacy. Herein, a facile and precise surface-enhanced scattering (SERS) approach based on coupled plasmonic field has been introduced to evaluate the therapeutic outcomes of antileukemia drug through ultrasensitive assay of caspase-3 activity in apoptotic cells. Caspase-3 as an apoptosis indicator could specifically cleave the N-terminus of biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) immobilized on the Au nanoparticle-decorated TiO 2 nanotube arrays (TiO 2 /Au NTAs) substrate. After the enzyme cleavage with caspase-3, Raman-labelled Au nanostar (AuNS) probes captured the residual DEVD-peptides via the recognition between streptavidin and biotin, thus resulting in an enhanced Raman response on the SERS platform. The variation of Raman intensity revealed caspase-3 activity that reflected the chemotherapeutic effect. On this platform, AuNS nanoprobes offered a large number of binding sites and intrinsic “hot spots” for Raman reporters, while TiO 2 /Au NTAs rendered a homogenously coupled electromagnetic field between the adjacent repeated units over the large area. In particular, a spatially expanding plasmonic field formed by coupling AuNSs with TiO 2 /Au NTAs would further heighten Raman enhancement. Taking these advantages, the strong and uniform Raman signals were achieved. Furthermore, the practicability investigation witnessed that the proposed SERS strategy was available to evaluate the therapeutic effect of dasatinib on CML K562 cells. The developed method possesses fascinating advantages of cost-effectiveness, excellent reproducibility and high sensitivity, which endows it with promising potential in apoptosis monitoring and anticancer drug development. [ABSTRACT FROM AUTHOR]

Sensitive and specific detection of DNA is of great significance for clinical diagnosis. In this paper, an effective cascade signal amplification strategy was introduced into photoelectrochemical (PEC) biosensor for ultrasensitive detection of human T-cell lymphotropic virus type I (HTLV-I) DNA. This proposed signal amplification strategy integrates λ-exonuclease (λ-Exo) aided target recycling with hybridization chain reaction (HCR) and enzyme catalysis. In the presence of target DNA (tDNA) of HTLV-I, the designed hairpin DNA (h 1 DNA) hybridized with tDNA, subsequently recognized and cleaved by λ-Exo to set free tDNA. With the λ-Exo aided tDNA recycling, an increasing number of DNA fragments (output DNA, oDNA) were released from the digestion of h 1 DNA. Then, triggered by the hybridization of oDNA with capture DNA (cDNA), numerous biotin-labeled hairpin DNAs (h 2 DNA and h 3 DNA) could be loaded onto the photoelectrode via the HCR. Finally, avidin-labeled alkaline phosphatase (avidin-ALP) could be introduced onto the electrode by specific interaction between biotin and avidin. The ALP could catalyze dephosphorylation of phospho-L-ascorbic acid trisodium salt (AAP) to generate an efficient electron donor of ascorbic acid (AA), and thereby greatly increasing the photocurrent signal. By utilizing the proposed cascade signal amplification strategy, the fabricated PEC biosensor exhibited an ultrasensitive and specific detection of HTLV-I DNA down to 11.3 aM, and it also offered an effective strategy to detect other DNAs at ultralow levels. [ABSTRACT FROM AUTHOR]

In the present work, electrogenerated chemiluminescence (ECL) of luminol was investigated in neutral condition at a gold electrode in the presence of silicon quantum dots (SiQDs). The results revealed that SiQDs can not only greatly enhance luminol ECL, but also act as energy acceptor to construct a novel ECL resonance energy transfer (ECL-RET) system with luminol. As a result, strong anodic ECL signal was obtained in neutral condition at the bare gold electrode, which is suitable for biosensing application. Lysozyme exhibited apparent inhibiting effect on the ECL-RET system, based on which an ECL aptasensor was fabricated for the sensitive detection of lysozyme. The proposed method showed high sensitivity, good selectivity, and wide linearity for the detection of lysozyme in the range of 5.0×10 –14 −5.0×10 −9 g mL −1 with a detection limit of 5.8×10 –15 g mL −1 (3σ). The results suggested that as-proposed luminol/SiQDs ECL biosensor will be promising in the detection enzyme. [ABSTRACT FROM AUTHOR]

An ultrasensitive electrochemiluminescence (ECL) biosensor for the detection of microRNA was developed based on nicking enzymes Nb.BbvCI mediated signal amplification (NESA). First, the hairpin probe1-N-CQDs with assistant probe and microRNA (miRNA) formed Y junction structure which was cleaved with the addition of nicking enzymes Nb.BbvCI to release miRNA and assistant probe. Subsequently, the released miRNA and assistant probe can initiate the next recycling process. The generation of numerous intermediate sequences nitrogen doped carbon quantum dots-DNA (N-CQDs-DNA) can further hybridize with hairpin probe2 immobilized on GO/Au composite modified electrode surface, the initial ECL intensity was enhanced. The ECL intensity would increase with increasing concentration of the target miRNA, and the sensitivity of biosensor would be promoted because of the efficient signal amplification of the target induced cycling reaction. The novel designed biosensor provided a highly sensitive and selective detection of miRNA-21 from 10 aM to10 4 fM with a relatively low detection limit of 10 aM. Thus, our strategy has a potential application in the clinical diagnosis. [ABSTRACT FROM AUTHOR]

Electrogenerated chemiluminescence (ECL) of semiconductor quantum dots (QDs) has been considered as a powerful technique in the fabrication of biosensor, however, high-toxicity of heavy metal ion containing in QDs severely limits their further applications, and the search for the alternative benign nanomaterials with high ECL efficiency is urgent. Herein, ECL behavior of eco-friendly silicon quantum dots (SiQDs) was reported in neutral aqueous condition. Stable and intense cathodic ECL emission was obtained in phosphate buffer solution (PBS) with K 2 S 2 O 8 as coreactant. ECL resonance energy transfer (ECL-RET) system was established with SiQDs ECL as energy donor and gold nanoparticles (AuNPs) as energy acceptor, based on which a novel ECL biosensor was fabricated. AuNPs was connected at the terminal of hairpin DNA to form a signal probe. When the probe was modified on SiQDs, ECL-RET occurred due to the short distance between AuNPs and SiQDs, resulting in the apparent decrease of ECL signal. Target DNA can open the loop of hairpin DNA, and move AuNPs away from the electrode surface. As a result, the ECL-RET process was hampered, and the ECL emission resumed. The increased ECL signals varied linearly with the target DNA concentrations in the range of 0.1 fM to 1 pM with the detection limit of 0.016 fM (3σ). The proposed ECL sensor exhibited highly sensitivity and good selectivity in the detection of target DNA. [ABSTRACT FROM AUTHOR]

Quantifying the glycan expression status on cell surfaces is of vital importance for insight into the glycan function in biological processes and related diseases. Here we developed a versatile aptasensor for electrochemical quantification of cell surface glycan by taking advantage of the cell-specific aptamer, and the lectin-functionalized gold nanoparticles acting as both a glycan recognition unit and a signal amplification probe. To construct the aptasensor, amine-functionalized mucin 1 protein (MUC1) aptamer was first covalently conjugated to carboxylated-magnetic beads (MBs) using the succinimide coupling (EDC-NHS) method. On the basis of the specific recognition between aptamer and MUC1 protein that overexpressed on the surface of MCF-7 cells, the aptamer conjugated MBs showed a predominant capability for cell capture with high selectivity. Moreover, a lectin-based nanoprobe was designed by noncovalent assembly of concanavalin A (ConA) on gold nanoparticles (AuNPs). This nanoprobe incorporated the abilities of both the specific carbohydrate recognition and the signal amplification based on the gold-promoted reduction of silver ions. By coupling with electrochemical stripping analysis, the proposed sandwich-type cytosensor showed an excellent analytical performance for the ultrasensitive detection of MCF-7 cells and quantification of cell surface glycan. More importantly, taking advantage of Con A-gold nanoprobe catalyzed silver enhancement, the proposed method was further used for naked-eye tracking glycolytic inhibition in living cells. This aptasensor holds great promise as a new point-of-care diagnostic tool for analyzing glycan expression on living cells and further helps cancer diagnosis and treatment. [ABSTRACT FROM AUTHOR]

MicroRNA-21 (miR-21) is a promising diagnostic biomarker for breast cancer screening and disease progression, thus the method for the sensitive and selective detection of miR-21 is vital to its clinical diagnosis. Herein, we develop a novel method to quantify miR-21 levels as low as attomolar sensitivity by a target-triggered triple isothermal cascade amplification (3TICA) strategy. An ingenious unimolecular DNA template with three functional parts has been designed: 5′-fragment as the miR-21 recognition unit, middle fragment as the miR-21 analogue amplification unit, and 3′-fragment as the 8–17 DNAzyme production unit. Triggered by miR-21 and accompanied by polymerase-nicking enzyme cascade, new miR-21 analogues autonomously generated for the successive re-triggering and cleavage process. Simultaneously, the 8–17 DNAzyme-contained sequence could be exponentially released and activated for the second cyclic cleavage toward a specific ribonucleotide (rA)-contained substrate, inducing a remarkably amplified generation of HRP-mimicking DNAzyme in the presence of hemin. Finally, the amperometric technique was used to record the catalytic reduction current of 3,3′,5,5′-tetramethylbenzidine (TMB) in the presence of H 2 O 2 . The increase in the steady-state current was proportional with the increase of the miR-21 concentration from 1 aM to 100 pM. An ultra-low detection limit of 0.5 aM with an excellent selectivity for even discriminating differences between 1-base mismatched target and miR-21 was achieved. This simple and cost-effective 3TICA strategy is promising for the detection of any short oligonucleotides, simply by altering the target recognition unit in the template sequence. [ABSTRACT FROM AUTHOR]

Since atherosclerosis, a disease characterized by abnormal arterial lipid deposition, may lead to fatal cardiovascular diseases, imaging of atherosclerotic plaques is of great value for their pathological assessment. In this study, we propose a lipid droplet (LD)-hitchhiking strategy to in situ create Trojan foam cells for fluorescence/photoacoustic imaging of atherosclerotic plaques via homologous targeting effect. In our design, functional liposomes (DCP liposomes) composed of phospholipid dioleoylphosphatidylserine (DOPS), a novel LD inducer we found, and Cypate-PC, a synthesized lipid-like molecular probe, have demonstrated great capability of inducing LDs in monocytes/macrophages while being enveloped into the resulting Trojan foam cells. Taking advantage of homologous targeting effect, the imaging probe hitchhikes on the LDs in Trojan foam cells for targeted transport to the plaque sites. Moreover, the confinement in highly hydrophobic LDs endows the imaging probe with high efficiency in light absorption, enabling greatly intensified fluorescence/photoacoustic signals. The DCP liposomes have shown great potency in inducing the generation of Trojan foam cells, and eventually ex vivo fluorescence imaging and in vivo photoacoustic imaging of atherosclerotic plaques. The proposed strategy provides more insights into the design of targeted imaging methodologies, and also an effective avenue to facilitate the evaluation and subsequent treatment of atherosclerotic plaques. • In situ lipid droplets formation in monocytes/macrophages (endocytosis of lipid). • Homologous targeting of Trojan foam cells to foam cells in atherosclerotic plaques. • Imaging probes hitchhiking on LDs in Trojan foam cells for atherosclerotic plaque targeting. • Hydrophobic LDs' environment elevating the light absorption efficiency of probes for combined FL/PA imaging. [ABSTRACT FROM AUTHOR]

A novel, enhanced photoelectrochemical immunoassay was established for sensitive and specific detection of carbohydrate antigen 19-9 (CA19-9, Ag). In this protocol, TiO 2 nanowires (TiO 2 NWs) were first decorated with Au nanoparticles to form TiO 2 NWs/Au hybrid structure, and then coated with CdSe@ZnS quantum dots (QDs) via the layer-by-layer method, producing TiO 2 NWs/Au/CdSe@ZnS sensitized structure, which was employed as the photoelectrochemical matrix to immobilize capture CA19-9 antibodies (Ab 1 ); whereas, bipyridinium (V 2+ ) molecules were labeled on signal CA19-9 antibodies (Ab 2 ) to form Ab 2 @V 2+ conjugates, which were used as signal amplification elements. The TiO 2 NWs/Au/CdSe@ZnS sensitized structure could adequately absorb light energy and dramatically depress electron–hole recombination, resulting in evidently enhanced photocurrent intensity of the immunosensing electrode. While target Ag were detected, the Ab 2 @V 2+ conjugates could significantly decrease the photocurrent detection signal because of strong electron-withdrawing property of V 2+ coupled with evident steric hindrance of Ab 2 . Thanks to synergy effect of TiO 2 NWs/Au/CdSe@ZnS sensitized structure and quenching effect of Ab 2 @V 2+ conjugates, the well-established photoelectrochemical immunoassay exhibited a low detection limit of 0.0039 U/mL with a wide linear range from 0.01 U/mL to 200 U/mL for target Ag detection. This proposed photoelectrochemical protocol also showed good reproducibility, specificity and stability, and might be applied to detect other important biomarkers. [ABSTRACT FROM AUTHOR]

A novel “ON–OFF” switchable enzymatic biofuel cell (EBFC), controlled by in situ thermal-stimuli signal, has been consciously designed. Poly ( N -isopropylacrylamide) (PNIPAm) chains were used to act as “ON” and “OFF” channels. Consecutively switching of temperature below and above the lower critical solution temperature (LCST), the reversible conformation changing of the PNIPAm chains between superhydrophilicity and superhydrophobicity was achieved, which constructed the “ON” and “OFF” channel for the transfer of the electrochemical probe to the underlying electrode correspondingly. Gold nanoparticles (AuNPs) protected glucose oxidase and laccase were successfully entrapped into the intelligent thermal-sensitive PNIPAm chains, and performed as the catalysts for the oxidation of glucose and the reduction of O 2 , respectively. Below the LCST, the fuels and the mediator could access to the catalytic centers of enzymes (set as “ON” state); while above the LCST, the reaction was impeded because the process of reactant transmission was blocked (set as “OFF” state). By switching the “valve” of mass transfer, the fabricated EBFC displayed the obvious “ON–OFF” controllable behavior. At the “ON” state, the open circuit voltage ( E cell ocv ) and maximal power output density ( P max ) could reach to 0.70 V and 20.52 μW cm −2 , respectively; while at the “OFF” state, the E cell ocv and P max were only 0.30 V and 3.28 μW cm −2 correspondingly. The switchable process was repeatable, and the response time was only several minutes. [ABSTRACT FROM AUTHOR]

A triple-signal amplification strategy was proposed for highly sensitive and selective detection of thymine DNA glycosylase (TDG) by coupling a dendrimer-like DNA label with the electrochemical method and quantum dots (QDs) tagging. The DNA-QDs dendrimer-like superstructure was designed by DNA hybridization and covalent assembling. Benefiting from outstanding performance of the amplification strategy, this assay showed high sensitivity, extraordinary stability, and easy operation. The limit of detection could reach 0.00003 U µL −1 with a splendid specificity. The TDG content in different concentration of HeLa cell was also determined. This assay opens a new horizon for both qualitative and quantitative detection of TDG, holding great promise for potential application in cancer cell research and clinical diagnostics. [ABSTRACT FROM AUTHOR]

A novel electrochemical biosensing platform for nicotinamide adenine dinucleotide (NAD+)-dependent dehydrogenase catalysis was designed using the nitrogen-doped graphene (NG), which had properties similar to NADH dehydrogenase (CoI). NG mimicked flavin mononucleotide (FMN) in CoI and efficiently catalyzed NADH oxidation. NG also acted as an electron transport "bridge" from NADH to the electrode due to its excellent conductivity. In comparison with a bare gold electrode, an 800mV decrease in the overpotential for NADH oxidation and CoI-like behavior were observed at NG-modified electrode, which is the largest decrease in overpotential for NADH oxidation reported to date. The catalytic rate constant (k) for the CoI-like behavior of NG was estimated to be 2.3×105M−1s−1, which is much higher than that of other previously reported FMN analogs. The Michaelis-Menten constant (Km) of NG was 26μM, which is comparable to the Km of CoI (10μM). Electrodes modified with NG and NG/gold nanoparticals/formate dehydrogenase (NG/AuNPs/FDH) showed excellent analytical performance for the detection of NADH and formate. This electrode fabrication strategy could be used to create a universal biosensing platform for developing NAD+-dependent dehydrogenase biosensors and biofuel cells. [ABSTRACT FROM AUTHOR]

In recent decades, advanced therapies and novel scientific drug evaluation systems for chronic myeloid leukemia (CML) treatment are very urgent due to its increasing morbidity. The combination of dasatinib with tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) was supposed to be effective for leukemia therapy. Taking full advantage of novel nano-biotechnology, we have developed a robust electrochemical cytosensing approach to profile the therapeutic effects of dasatinib and TRAIL by probing the activity of caspase-3 from apoptotic CML cells. The sensor was on a base of a glassy carbon electrode (GCE) modified with nano-materials composed of Au nanoparticles (AuNPs), poly(dimethyl diallyl ammonium chloride) (PDDA), and carbon nanotubes (CNTs). Then the platform immobilized the biotinylated DEVD-peptide (biotin-Gly-Asp-Gly-Asp-Glu-Val-Asp-Gly-Cys) via the strong bonding between AuNPs and the thiol group (Au-S bond). In particular, the sensor was then constructed with the environmentally friendly alkaline phosphatase (ALP) via the specific interaction between the biotin and streptavidin, and could retest detection indirectly for caspase-3 sensing by detecting the differential pulse voltammetry (DPV) signal of enzymatic catalysis product, ascorbic acid (AA). The results indicated that either dasatinib or TRAIL could successfully induce the apoptosis of CML cells, while the combination of dasatinib and TRAIL resulted in an improved therapeutic effect, suggesting a novel optimized strategy for CML therapy. This novel electrochemical sensing strategy exhibits attractive advantages of environmental benignity, simple performance, high stability, and may be readily expanded to evaluate other cancer therapeutic effects. [ABSTRACT FROM AUTHOR]

Abstract: Dual co-sensitized structure of TiO2/CdS/CdSe was designed to develop a novel photoelectrochemical immunoassay for highly sensitive detection of human interleukin-6 (IL-6). To construct a sensing electrode, TiO2/CdS hybrid was prepared by successive adsorption and reaction of Cd2+ and S2− ions on the surface of TiO2 and then was employed as matrix for immobilization of anti-IL-6 antibody, whereas CdSe QDs linked to IL-6 were used for signal amplification via the specific antibody–antigen immunoreaction between anti-IL-6 and IL-6–CdSe bioconjugate. Greatly enhanced sensitivity for IL-6 detection was derived from the new co-sensitization signal amplification strategy. First, the TiO2/CdS/CdSe co-sensitized structure extended the absorption range to long wavelength of white light, which adequately utilized the light energy. Second, the TiO2/CdS/CdSe co-sensitized structure possessed stepwise band-edge levels favoring ultrafast transfer of photogenerated electrons and significantly prompted the photoelectrochemical performance. Besides, the introduction of CdSe effectively prevented the recombination of photogenerated electrons in the conduction band of CdS, further causing an enhanced photocurrent. Accordingly, upon the co-sensitization strategy, a novel immunoassay based on the competitive binding of anti-IL-6 antibody with IL-6 antigen and IL-6–CdSe bioconjugate was developed, and it exhibited a wide linear range from 1.0pg/mL to 100ng/mL with a low detection limit of 0.38pg/mL for IL-6 detection. The proposed co-sensitization strategy presented high sensitivity, reproducibility, specificity and stability, and also opened up a new promising platform for detection of other biomarkers. [Copyright &y& Elsevier]

Abstract: An ultrasensitive electrochemical immunoassay was developed for rapid detection of interleukin-6 (IL-6) and matrix metallopeptidase-9 (MMP-9); the method utilized PS@PDA-metal nanocomposites based on graphene nanoribbon (GNR)-modified heated screen-printed carbon electrode (HSPCE). Because of the good hydrophilicity and low toxicity, GNRs were used to immobilize antibodies (Ab) and amplify the electrochemical signal. PS@PDA-metal was used to label antibodies and generate a strong electrochemical signal in acetic buffer. A sandwich strategy was adopted to achieve simultaneous detection of MMP-9 and IL-6 based on HSPCE without cross-talk between adjacent electrodes in the range of 10−5 to 103 ngmL−1 with detection limits of 5fgmL−1 and 0.1pgmL−1 (S/N=3), respectively. The proposed method showed wide detection range, low detection limit, acceptable stability and good reproducibility. Satisfactory results were also obtained in the practical samples, thus showing this is a promising technique for simultaneous clinical detection of biocomponent proteins. [Copyright &y& Elsevier]

Abstract: A novel microfluidic platform integrated with a flexible PDMS-based electrochemical cytosensor was developed for real-time monitoring of the proliferation and apoptosis of HeLa cells. The PDMS-gold film, which had a conductive smooth surface and was semi-transparent, facilitated electrochemical measurements and optical microscope observations. We observed distinct increases and decreases in peak current intensity, corresponding to cell proliferation in culture medium and apoptosis in the presence of an anticancer drug, respectively. This electrochemical analysis method permitted real-time, label-free monitoring of cell behavior, and the electrochemical results were confirmed with optical microscopy. The flexible microfluidic electrochemical platform presented here is suitable for on-site monitoring of cell behavior in microenvironments. [Copyright &y& Elsevier]

Abstract: A sensitive electrochemical immunosensor with graphene-assisted signal amplification has been developed. In order to construct the base of the immunosensor, a novel hybrid architecture was initially fabricated by combining poly (diallyldimethylammonium chloride) functionalized graphene nanosheets (PDDA-G) and gold nanoparticles (AuNPs) via a simple sonication-induced assembly. The formed hybrid architecture provided an effective matrix for antibody immobilization with good stability and bioactivity. Subsequently, a smart, multilabel, and graphene-based nanoprobe that contains gold nanoparticles functionalized exfoliated graphene oxide and horseradish peroxidase-secondary antibodies was designed for constructing a novel sandwiched electrochemical immunosensor. Enhanced sensitivity was obtained by combining the advantages of high-binding capability and excellent electrical conductivity of hybrid architecture with the multilabel signal amplification. On the basis of the dual signal amplification strategy of graphene-based architecture and the multilabel, the immunosensor displayed excellent analytical performance for the detection of human IgG (HIgG) range from 0.1 to 200ng/mL with a detection limit of 0.05ng/mL at 3σ. Moreover, the proposed method showed good precision, acceptable stability and reproducibility, and could be used for the detection of HIgG in real samples. Therefore, the present strategy definitely paves a way for the wide application of graphene in clinical research. [Copyright &y& Elsevier]

Abstract: A sensitive colorimetric detection for biomolecules based on aptamer was described. Poly(dimethylsiloxane) (PDMS)–gold nanoparticles (AuNPs) composite film was used as a platform for immobilizing anti-target aptamer. PDMS–AuNPs composite film only covered with aptamer showed high inhibiting ability towards silver reduction, after target molecules were conjugated on the modified surface, the catalytic efficiency of AuNPs for silver reduction was increased. In this system, the darkness density of silver enhancement was applied for target quantitative measurement. Lysozyme and adenosine 5′-triphosphate (ATP) were tested as the models, quantitative measurements with imaging software or semiquantitative measurements with naked eyes were carried out in the range of 1×10−2–1μg/mL and 1×10−4–1×103 μg/mL, the volume of reagent using in each assay is 15μL or less. We speculated that aptamer-target conjugates’ inhibition ability for AuNPs’ catalytic efficiency toward silver reduction might come from charge and spatial effects. This study can offer a completely novel and relatively general approach for colorimetrical aptamer sensors with good analytical properties and potential applications. The sensor could be coupled with digital transmission of images for remote monitoring system in diagnosis, food control, and environmental analysis. [Copyright &y& Elsevier]

Abstract: A novel immunosensor for sensitive detection of tumor necrosis factor α was reported. First of all, gold nanoparticles were uniformly assembled on the surface of poly (styrene-acrylic acid) nanospheres, which was used as the matrix to conjugate alkaline phosphatase (ALP). And then, the obtained composite was used as multi-enzyme functionalized label for immunoassay. Biocompatible polyaniline doped with poly (acrylic acid) was electro-polymerized at the glass carbon electrode to construct the matrix for the immobilization of antibody TNF-α. After the sandwich immunoreaction, the labeled ALP was used to hydrolyze α-naphthyl phosphate to produce the electroactive α-naphthol, which could be amperometrically detected. The results showed that the electrochemical signals were proportional to the logarithm of the antigen concentration in the range of 0.02–200.00ng/mL with the detection limit of 0.01ng/mL. The developed immunoassay showed high sensitivity, acceptable stability and reproducibility, which might have potentially broad applications in protein diagnostics and bioassay. [ABSTRACT FROM AUTHOR]

Abstract: A sensitive electrochemical aptasensor was successfully fabricated for the detection of adenosine triphosphate (ATP) by combining three-dimensionally ordered macroporous (3DOM) gold film and quantum dots (QDs). The 3DOM gold film was electrochemically fabricated with an inverted opal template, making the active surface area of the electrode up to 9.52 times larger than that of a classical bare flat one. 5′-Thiolated ATP-binding aptamer (ABA) was first assembled onto the 3DOM gold film via sulfur–gold affinity. Then, 5′-biotinated complementary strand (BCS) was immobilized via hybridization reaction to form the DNA/DNA duplex. Since the tertiary structure of the aptamer was stabilized in the presence of target ATP, the duplex can be denatured to liberate BCS. The reaction was monitored by electrochemical stripping analysis of dissolved QDs which were bound to the residual BCS through biotin–streptavidin system. The decrease of peak current was proportional to the amount of ATP. The unique interconnected structure in 3DOM gold film along with the “built-in” preconcentration remarkably improved the sensitivity. ATP detection with high selectivity, wide linear dynamic range of 4 orders of magnitude and high sensitivity down to 0.01nm were achieved. The results demonstrated that the novel strategy was feasible for sensitive ATP assay and provided a promising model for the detection of small molecules. [ABSTRACT FROM AUTHOR]

Abstract: A novel mediator-free biosensor was constructed by the co-intercalation of negatively charged DNA and positively charged hemoglobin (Hb) in the interlayer galleries of layered α-zirconium phosphate (α-ZrP) with the delamination-assembly procedure at pH 5.5. X-ray diffraction and field-emission scanning electron microscopy results revealed the featured layered structure for the re-assembled DNA/Hb/α-ZrP composite. Infrared spectroscopy and circular dichroism results confirmed the coexistence of Hb and DNA in the composite and the considerably retained protein conformation of intercalated Hb. The direct electron transfer of Hb was facilitated by the co-intercalation of DNA and Hb. Because of the synergistic effect of α-ZrP host and co-intercalated DNA guest, the DNA/Hb/α-ZrP modified electrode exhibited good electrocatalytic response to H2O2 with higher sensitivity of 0.79AM−1 cm−2 and lower detection of 4.28×10−7 M in the linear range of 7.28×10−7 to 9.71×10−5 M. Furthermore, the electrocatalytic activity of Hb in the DNA/Hb/α-ZrP composite retained at high temperature (85°C) or in the presence of organic solvent (CH3CN), which could be the protection of α-ZrP nanosheets. [Copyright &y& Elsevier]

Abstract: A simple strategy for sensitive detection of human IgG using cadmium ions-functionalized polymer nanospheres as the label is presented. The polymer nanosphere consisted of hard poly-styrene core and biocompatible poly (acrylic acid) (PAA) shell. The carboxyl groups of hydrophilic shell were used to chelated with the cadmium ions, and then conjugate with antibody (Ab2) to fabricate metal ions marked bioconjugates as the label in immunoassay. For constructing the matrix of the immunosensor, the PAA-functionalized carbon nanotubes were used to modify disposable screen printed electrodes for the immobilization of antibody (Ab1). After sandwich immunoreaction, differential pulse voltammetry was used to oxidize the conjuncted cadmium for the detection of antigen. The obtained results provided a linear response range from 0.1 to 35.0pg/mL human IgG with a lower detection limit of 0.06pg/mL, which is prominently improved in comparison with conventional immunoassay. The usage of the chelation reaction offers a simple and convenient route for the preparation of metallo-immunoassay labels, and also avoids the complicated and time-consuming dissolving of metal component for ultrasensitive determination. This approach is expected to have wide applications in protein diagnostics and bioanalysis in the future. [Copyright &y& Elsevier]

Abstract: A novel type of colloidal carbon sphere array (CSA) was developed for the fabrication of disposable electrochemical immunosensor. The CSA was successfully prepared on indium tin oxide (ITO) substrate in a simple manner and the scanning electron micrograph confirmed that a single-layered arrangement of the carbon spheres with its (111) plane paralleled the substrate''s surface. The CSA modified electrode has a higher surface area and exhibits a more sensitive electrochemical response than a normal carbon-based electrode with the same geometric area. An Immunoglobin A (IgA) immunosensor was constructed by the covalent bonding of IgA antibody molecules with the CSA aided by large numbers of carboxyl groups on the surface of carbon spheres. The immunosensor exhibited a wide linear response to IgA ranging from 0.1 to 200ngmL−1 by electrochemical impedance spectroscopy (EIS) technique. The detection of IgA levels in three sera obtained from hospital samples showed acceptable accuracy. [Copyright &y& Elsevier]

Abstract: A novel sensing system based on the near infrared (NIR) fluorescence resonance energy transfer (FRET) between Mn:CdTe quantum dots (Qdots) and Au nanorods (AuNRs) was established for the detection of human IgG. The NIR-emitting Qdots linked with goat anti-human IgG (Mn:CdTe-Ab1) and AuNRs linked with rabbit anti-human IgG (AuNRs-Ab2) acted as fluorescence donors and acceptors, respectively. FRET occurred by human IgG with the specific antigen–antibody interaction. And human IgG was detected based on the modulation in FRET efficiency. The calibration graph was linear over the range of 0.05–2.5μM of human IgG under optimal conditions. The proposed sensing system can decrease the interference of biomolecules in NIR region and increase FRET efficiency in optimizing the spectral overlap of AuNRs with Mn:CdTe Qdots. This method has great potential for multiplex assay with different donor–acceptor pairs. [Copyright &y& Elsevier]

Abstract: Electrochemiluminescence (ECL) of CdSe quantum dots (QDs) was greatly enhanced by the combination of carbon nanotubes (CNTs) and poly (diallyldimethylammonium chloride) (PDDA) in the CdSe QDs film, and could successfully be used to develop a sensitive ECL immunosensor for the detection of human IgG (Ag). The novel CdSe QDs–CNTs composites exhibited high ECL intensity, good biocompatibility, and high stability, which held great promise for the fabrication of the ECL biosensors with improved sensitivity. After PDDA as a binding linker was conjugated to the CdSe QDs–CNTs composite film on the electrode, the ECL signal was significantly enhanced. Subsequently, gold nanoparticles (GNPs) assembled onto the CdSe QDs–CNTs/PDDA modified electrode could amplify the ECL signal once again. After antibody (Ab) was immobilized onto the electrode through GNPs, the ECL immunosensor was successfully fabricated. It is for the first time that the unique function of PDDA for enhancing QDs ECL was explored and used to develop an ECL biosensor. The principle of ECL detection for target Ag is based on the increment of steric hindrance after immunoreaction, which resulted in the decrease of ECL intensity. The Ag concentration was determined in the linear range of 0.002–500ngL−1 with a detection limit of 0.6pgmL−1. The sensor showed good fabrication and detection reproducibility, and the assay results were in acceptable agreement with the clinical sera tests, showing a promising clinical application. This work opened the new avenues for applying QDs ECL in highly sensitive bioassays. [Copyright &y& Elsevier]

Abstract: We describe a non-labeled electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots (QDs) for the detection of human prealbumin (PAB, antigen). The immunosensor was fabricated by layer by layer coupled with nanoparticle-amplification techniques. After two gold nanoparticle layers were self-assembled onto the gold electrode surface through cysteamine, anti-PAB (antibody) were conjugated with –COOH groups of both the CdSe QDs and cysteine, which were linked to the gold nanoparticle-modified electrode. The principle of ECL detection was that the immunocomplex inhibited the ECL reaction between CdSe QDs and K2S2O8, which resulted in the decrease of ECL intensity. On the one hand, the immunocomplex increased the steric hindrance. On the other hand, the immunocomplex maybe inhibit the transfer of K2S2O8 to the surface of the CdSe QD-electrode. The PAB concentration was determined in the range of 5.0×10−10 to 1.0×10−6 gmL−1, and the detection limit was 1.0×10−11 gmL−1. The developed CdSe QD-based ECL immunosensor provides a rapid, simple, and sensitive immunoassay protocol for protein detection, which could be applied in more bioanalytical systems. [Copyright &y& Elsevier]

Abstract: This paper describes the combination of electrochemical immunosensor using gold nanoparticles (GNPs)/carbon nanotubes (CNTs) hybrids platform with horseradish peroxidase (HRP)-functionalized gold nanoparticle label for the sensitive detection of human IgG (HIgG) as a model protein. The GNPs/CNTs nanohybrids covered on the glass carbon electrode (GCE) constructed an effective antibody immobilization matrix and made the immobilized biomolecules hold high stability and bioactivity. Enhanced sensitivity was obtained by using bioconjugates featuring HRP labels and secondary antibodies (Ab2) linked to GNPs at high HRP/Ab2 molar ratio. The approach provided a linear response range between 0.125 and 80ng/mL with a detection limit of 40pg/mL. The immunosensor showed good precision, acceptable stability and reproducibility and could be used for the detection of HIgG in real samples, which provided a potential alternative tool for the detection of protein in clinical laboratory. [Copyright &y& Elsevier]

Abstract: Gold nanoparticles (AuNPs) with an average diameter of 5nm were assembled on the surface of silver chloride@polyaniline (PANI) core-shell nanocomposites (AgCl@PANI). Attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) suggested that AuNPs were incorporated on AgCl@PANI through coordination bonds instead of electrostatic interaction. The resulting AuNPs–AgCl@PANI hybrid material exhibited good electroactivity at a neutral pH environment. An amperometric glucose biosensor was developed by adsorption of glucose oxidase (GOx) on an AuNPs–AgCl@PANI modified glassy carbon (GC) electrode. AuNPs–AgCl@PANI could provide a biocompatible surface for high enzyme loading. Due to size effect, the AuNPs in the hybrid material could act as a good catalyst for both oxidation and reduction of H2O2. As the measurement of glucose was based on the electrochemical detection of H2O2 generated by enzyme-catalyzed-oxidation of glucose, the biosensor exhibited a super highly sensitive response to the analyte with a detection limit of 4pM. Moreover, the biosensor showed good reproducibility and operation stability. The effects of some factors, such as temperature and pH value, were also studied. [Copyright &y& Elsevier]

Abstract: The nanocomposite composed of carboxymethyl chitosan (CMCS) and gold nanoparticles was successfully prepared by a novel and in situ process. It was characterized by transmission electron microscopy (TEM) and Fourier transform infrared spectrophotometer (FTIR). The nanocomposite was hydrophilic even in neutral solutions, stable and inherited the properties of the AuNPs and CMCS, which make it biocompatible for enzymes immobilization. HRP, as a model enzyme, was immobilized on the silica sol–gel matrix containing the nanocomposite to construct a novel H2O2 biosensor. The direct electron transfer of HRP was achieved and investigated. The biosensor exhibited a fast amperometric response (5s), a good linear response over a wide range of concentrations from 5.0×10−6 to 1.4×10−3 M, and a low detection limit of 4.01×10−7 M. The apparent Michaelis–Menten constant () for the biosensor was 5.7×10−4 M. Good stability and sensitivity were assessed for the biosensor. [Copyright &y& Elsevier]

Abstract: A novel organic–inorganic nanocomposite of methylene blue (MB) and silicon oxide was synthesized and characterized by TEM, FTIR, and UV–vis. The as-prepared material was able to transfer the electron of the MB to electrode and was different from other SiO2 spheres structurally. It can be used as mediator to construct a biosensor with horseradish peroxidase (HRP) coimmobilized in the gelatine matrix and cross-linked with formaldehyde. The resulting biosensor exhibited fast amperometric response and good stability to hydrogen peroxide (H2O2). The linear range for H2O2 determination was from 1×10−5 to 1.2×10−3 M, with a detection limit of 4×10−6 M based on S/N=3. Moreover, the lifetime is more than 3 months under dry conditions at 4°C. [Copyright &y& Elsevier]