Search

In this work, a novel and facile electrochemical sensor is reported for the highly selective and sensitive detection of dissolved hydrogen sulfide (H 2 S), attributing to the redox reaction between Au@Ag core-shell nanoparticles (Au@Ag NPs) and H 2 S. Electroactive Au@Ag NPs not only possess excellent conductivity, but exhibit great electrochemical reactivity at 0.26 V due to the electrochemical oxidation from Ag° to Ag + . In the presence of H 2 S, the Ag shell of Au@Ag NPs can be oxidized to Ag 2 S, resulting in the decrease of differential pulse voltammetry (DPV) peak at 0.26 V. The electrochemical sensor exhibits a wide linear response range from 0.1 nM to 500 nM. The limit of detection (LOD) for H 2 S is as low as 0.04 nM. The developed sensor shows significant prospects in the study of pathological processes related to the mechanism of H 2 S production. [ABSTRACT FROM AUTHOR]

Graphene quantum dot (GQD) has been attractive in analytical science field due to its low toxicity, stable photoluminescence. Herein, nitrogen-doped GQD (N-GQD) was prepared by a facile solvothermal treatment of GO using dimethylformamide, and exhibited a green emission with 23.1% quantum yield. The N-GQD probe showed a selective and sensitive fluorescence enhancement response to Al 3+ , the mechanism might be the formation of a complex between Al 3+ and N-GQD constrained the photo-induced electron transfer (PET) process of N-GQD itself. With Benesi-Hildebrand equation, the binding constant and molar ratio between N-GQD and Al 3+ was calculated to be 4.6 × 10 4 L mol −1 and 1:1 respectively. The p K a value of N-GQD was also determined to be 4.4 by capillary electrophoresis. In pH 4.0 PBS solution, there was a good linear relation between the fluorescence intensity and the logarithm of concentration of Al 3+ in the range of 2.5–75 μmol L −1 , the limit of detection (3σ) was 1.3 μmol L −1 . This “Off - On” fluorescence method had been applied to accurate quantification of aluminum in hydrotalcite tablets. What's more, the fluorescence switch property of N-GQD was explored by alternate addition of Al 3+ and EDTA. The probe was also utilized for detection Al 3+ in living cells due to its excellent biocompatibility. [ABSTRACT FROM AUTHOR]

The exploration of electroactive labelling with tailorable and strong differential pulse voltammetry (DPV) responses is of great importance in accurate and sensitive screening of a panel of biomarkers related to cancer. Herein, shell-encoded gold nanoparticles (Au NPs) are fabricated and give rise to shell species-dominated DPV peak potentials. Two independent DPV peaks appear at −0.08 V for Au@Cu 2 O core-shell NPs and 0.26 V for Au@Ag core-shell NPs. Shell-encoded Au NPs drastically exhibit shell thickness-tunable amplified peak currents. The non-interfering and amplified DPV responses enable shell-encoded Au NPs to be an alternative electrochemical signal amplifier for dual screening of carcinoembryonic antigen (CEA) and alpha-fetoprotein (AFP). The limits of detection (LODs) are calculated to be 1.8 pg/mL for CEA and 0.3 pg/mL for AFP. In comparison to the parallel single-analyte assays, shell-encoded Au NPs engineered electrochemical aptasensors offer multiplexing capability and show significant prospects in biomedical research and early diagnosis of diseases. [ABSTRACT FROM AUTHOR]

Growing studies focusing on nuclear acid detection via the emerging CRISPR technique demonstrate its promising application. However, limited works solve the identification of non-nucleic acid targets, especially multiple small molecules. To address challenges for point-of-care testing (POCT) in complex matrices for healthcare, environment, and food safety, we developed CRISPR Cas12a-powered highly sensitive, high throughput, intelligent POCT (iPOCT) for multiple small molecules based on a smartphone-controlled reader. As a proof of concept, aflatoxin B1 (AFB1), benzo[a]pyrene (BaP), and capsaicin (CAP) were chosen as multiple targets. First, three antigens were preloaded in independent microwells. Then, the antibody/antigen-induced fluorescent signals were consecutively transferred from the biotin-streptavidin to CRISPR/Cas12a system. Third, the fluorescent signals were recorded by a smartphone-controlled handheld dark-box readout. Under optimization, detection limits in AFB1, BaP, and CAP were 0.00257, 4.971, and 794.6 fg/mL with wide linear ranges up to four orders of magnitude. Using urine, water, soybean oil, wheat, and peanuts as the complex matrix, we recorded high selectivity, considerable recovery, repeatability, and high consistency comparison to HPLC-MS/MS methods. This work promises a practical intelligent POCT platform for multiple targets in lipid-soluble and water-soluble matrices and could be extensively applied for healthcare, environment, and food safety. An intelligent CRISPR/Cas12-empowered immune biosensor was developed for detecting aflatoxin B1, benzo[a]pyrene, and capsaicin in clinical, environmental, and food samples via a smartphone-controlled handheld dark-box readout. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: Surface stress-based biosensors, as one kind of label-free biosensors, have attracted lots of attention in the process of information gathering and measurement for the biological, chemical and medical application with the development of technology and society. This kind of biosensors offers many advantages such as short response time (less than milliseconds) and a typical sensitivity at nanogram, picoliter, femtojoule and attomolar level. Furthermore, it simplifies sample preparation and testing procedures. In this work, progress made towards the use of surface stress-based biosensors for achieving better performance is critically reviewed, including our recent achievement, the optimally circular membrane-based biosensors and biosensor array. The further scientific and technological challenges in this field are also summarized. Critical remark and future steps towards the ultimate surface stress-based biosensors are addressed. [Copyright &y& Elsevier]

Strong and stable electrochemical beacons are critical for the achievement of sensitive and reliable electroanalysis applications. In this work, the electrochemical oxidation performance of AuPt NPs was studied and firstly found to be largely enhanced under light illumination. Plasmonic AuPt NPs collected light energy after local surface plasmon resonance (LSPR) excitation and generated much more holes to participate in the electrochemical oxidation process of Pt0 in AuPt NPs. AuPt NPs with the electrochemical oxidation peak at around −0.7 V were utilized as detection probes for the fabrication of ratiometric electrochemical aptasensor, by introducing Co-MOF/Fe 3 O 4 /Ag nanosheets (NSs) with the electrochemical oxidation peak at 0.1 V as reference beacons. The aptamers of epithelial cell adhesion molecule (EpCAM) modified AuPt NPs were assembled with Co-MOF/Fe 3 O 4 /Ag NSs, which generated strong detection and reference signals at −0.7 V and 0.1 V, respectively. The high affinity between EpCAM and aptamers induced the separation of AuPt NPs from Co-MOF/Fe 3 O 4 /Ag NSs, resulting in the decrease of detection signal at −0.7 V and unchanged reference signal at 0.1 V. A ratiometric electrochemical aptasensor was achieved for the sensitive and reliable quantification of EpCAM in the range from 100 pg/mL to 100 ng/mL. The limit of detection (LOD) was calculated to be 13.8 pg/mL for EpCAM. Plasmon-driven electrochemical oxidation enhancement principle provides the possibility for the design and fabrication of more strong and anti-interference electroactive plasmonic metal-Pt composite nanostructures for the electroanalysis applications. • AuPt alloy NPs exhibit electro-oxidization peaks at −0.7 V. • AuPt NPs show amplified electro-oxidization activity under LSPR excitation. • The proposed plasmon-promoted electro-oxidization principle is verified. • AuPt NPs driven electrochemical aptasensor is established for EpCAM detection. [ABSTRACT FROM AUTHOR]

In the study, we have developed an efficient and robust method using dual modes of fluorescence sensing and smartphone readout for the detection of pyrethroids using artificial receptors inside a covalent organic framework. Carbazole-conjugated frameworks (CCFs) were used to prepare efficient fluorescent probes that combine stability with light-emitting activity. C N linkages between aldehydes and amines formed Schiff bases, allowing the development of layered structures, creating exceptionally stable frameworks. Artificial receptors that can bind compounds inside the CCFs with high affinity, for both the detection and absorption of λ-cyhalothrin (LC), were constructed using room-temperature reverse microemulsion polymerization. Under optimum conditions, the fluorescence sensing correlation with the concentration of LC showed good linearity in the range of 0.8–175 μg L−1 with a detection limit of 0.368 μg L−1. The smartphone-based visible readout exhibited a good effect, with a detection limit of 4.067 μg L−1, and recovery of 88 %–103% in food samples. A parallel analysis in food samples was conducted by high-performance liquid chromatography, the results showed good consistency, indicating the practicability of the developed method. Dual mode analysis can avoid the disadvantages of a single response, providing excellent sensitivity, specificity, and efficiency through a strong binding force between the target and the artificial receptors. [Display omitted] • Efficient and robust dual modes of fluorescence sensing and smartphone readout for the detection of pyrethroids. • Dual mode analysis using artificial receptors bound inside a covalent organic framework. • Carbazole-conjugated frameworks were used to prepare efficient fluorescent probes. • The on/off fluorescence of the target-CCFs complex was reversible. • Dual mode analysis provide excellent sensitivity, specificity, and efficiency. [ABSTRACT FROM AUTHOR]

In this work, gigahertz solidly mounted resonators (SMRs) (2.5 GHz) were designed and fabricated to construct a novel particle-resonator system to achieve the biomolecular stiffness sensing in real time. The positive frequency shift of the system was used to estimate the stiffness of biomolecules connecting between the SMR and attached particles. The working principle was revealed by the mathematical analysis of the general block-spring model of the system. Further interpretations about the mechanism of such elastic interaction from the perspective of acoustic resonant modes of SMRs were given by finite element method. Biotin-streptavidin, antibody and antigen binding system were used as model molecular linkers to study the frequency shift varied with different particle diameters and particle densities. Different linker stiffness was realized by adjusting the concentrations of antigens connected with particles which form specific binding with antibodies immobilized on the SMR. The results fairly agree with the simulation results demonstrating the proposed particle-resonator system as an effective method to realize the real-time biomolecular stiffness detection. [ABSTRACT FROM AUTHOR]

Abstract: The interface behavior and biocatalytic activity of superoxide dismutase (SOD) were studied at carbon nanotube (CNT) surface with cyclic voltammetry (CV). The results show that SOD participates in a rapid exchange with CNT and the process is a single-electron–single-proton process. The electron-transfer coefficient was calculated to be 0.52, the electron-transfer rate constant was 1.4s−1 and the average surface coverage was measured to be 6.93×10−11 ±4.2×10−12 molcm−2. The bioactive measurements show that SOD keeps its bioactivity at the CNT surface. SOD''s remarkable ability to catalyze the dismutation of the superoxide anion () has been demonstrated. [Copyright &y& Elsevier]

We report a triplex signal amplification strategy for sensitive biosensing of cancer biomarker by taking advantage of hairpin-shaped oligonucleotide-functionalized gold nanorods (HO-GNRs), graphene and the avidin-biotin reation. The strategy expands electrochemical detection of carcinoembryonic antigen (CEA) by using an aptamer as biosensor's recognition element and HO-GNRs as signal enhancer. To construct this biosensor, the GNR was used as a carrier of horseradish peroxidase (HRP) and HO aptamer with a biotin at the 3′-end and a thiol at the 5′-end, which amplified the electrochemical response because of a large molar ratio of HRP to HO. In the presence of target CEA, the binding reactions of CEA with the loop portions of the HOs caused HOs’ loop-stem structure opened and exposed the biotins, and then HRP-GNRs-HO conjugates were captured on graphene and streptavidin modified electrodes via the reaction between the exposed biotins and preimmobilized streptavidins. The accumulation of HRP effectively catalyzed the hydrogen peroxide-mediated oxidation of o -phenylenediamine to generate an electrochemical reduction current for CEA detection. Under optimal conditions, the electrochemical biosensor exhibited a wide dynamic range of 5 pg mL −1 and 50 ng mL −1 toward CEA standards with a low detection limit of 1.5 pg mL −1 (signal-to-noise ratio of 3). The proposed biosensor accurately detected CEA concentration in 8 human serum samples from patients with lung diseases, showing excellent correlations with standard chemiluminescence immunoassay. Furthermore, these results of target DNA detection made it abundantly clear that the proposed strategy can also be extended for detection of other relative biomarkers using different functional DNA structures, which shows great prospects in single-nucleotide polymorphisms analysis, biomedical sensing and application for accurate clinical diseases diagnostic. [ABSTRACT FROM AUTHOR]

Contaminant residue analysis in milk can provide essential assistance for safety quality and contamination level management of milk production, which is critical for safeguarding public health. In this study, the pregnancy test strip is employed to achieve multiple analytes detection based on the specific recognition of aptamer and terminal deoxynucleotidyl transferase associated with split G-quadruplex/hemin deoxyribozyme system. Through the subsequent enzyme catalyzed reaction, the detection signal can be further amplified to improve the sensitivity. The method does not need to assemble test strip, prepare and purify antibodies/haptens, nor design complex probe sequences. By coupling human chorionic gonadotrophin with DNA probes and combining magnetic separation technology, the targets can be determined via the test strip. Under the optimized conditions, the visual detection limits for mercury ion, bisphenol A, and penicillin are 1, 0.1 and 0.05 nM, respectively. The detection results show that the method displays good accuracy and practicability in spiked milk sample. The method presents a simple scheme, low cost as well as good design versatility, which demonstrates great application prospect for the sensitive, low-cost, and convenient detection of food matrices. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The mixture of graphene oxide (GO) and aptamer labeled fluorophore is widely used in developing fluorescent sensors for the analysis of biomolecules, according to the light signal ‘off–on’ procedure. Moreover, the laser-induced fluorescence-coupled affinity probe capillary electrophoresis (APCE) technique has been broadly applied for the separation of micromolecules. Here, a strategy is proposed for analysis of content of carcino-embryonic antigen (CEA) based on the combination of GO and quantum dots labeling aptamer (QD–aptamer) by capillary electrophoresis (CE). The method has three advantages: (i) combined with CE, only few samples are required and efficiency of separation is high, (ii) fluorescent detection can be carried out after separation of GO and fluorescence probe combined with targets by CE, while fluorescence detection sensitivity had been greatly improved, and (iii) the issues of APCE, including the effect of excess fluorescence probe and maximizing separation between analytes, could be solved by introducing GO. It has been proved that QD–aptamer–CEA complex can completely dissociate from GO. Results show that the fluorescence intensity has a linear relationship with the concentration of CEA in the range from 0.257 to 12.9ng/mL, and the limit of detection is approximately 5pg/mL (S/N=3). The proposed method with high specificity has been applied for the accurate analysis of content of CEA in patient׳s serum. [Copyright &y& Elsevier]

Abstract: Single-walled carbon nanotubes (SWCNTs) and hemoglobin (Hb) modified carbon fiber ultramicroelectrode (CFUME) were employed to construct a direct electron transfer based in vivo H2O2 sensor. At the low working potential of −0.1V, Hb/SWCNTs/CFUME showed a dynamic range up to 0.405mM with a low detection limit of 4μM (S/N=3) and a high sensitivity of 1.07log(A) log(M)−1 cm−2. The apparent Michaelis–Menten constant (K m, app) was estimated to be as low as 1.35mM. Due to the extremely small dimension and low working potential, Hb/SWCNTs/CFUME could give directly amperometric in vivo monitoring of H2O2 in aloe leaves with salt stress for 19.5h without the requirement of complex data processing and extra surface coatings to avoid interferences. The sharp increase of H2O2 level in aloe leaves with salt stress was clearly observed using Hb/SWCNTs/CFUME from 12.5h, while in the aloe without salt stress, H2O2 level remained stable in the whole measurement. For further confirming the in vivo response of Hb/SWCNTs/CFUME, catalase (CAT) was injected into the spot adjacent to the sensor and caused rapid current decrease, which suggests the scavenging of H2O2. These results indicate that Hb/SWCNTs/CFUME can be a powerful tool for in vivo investigation of ROS. [Copyright &y& Elsevier]

Abstract: Here a novel capillary electrophoresis (CE) for simultaneous detection of dual single-base mutations using quantum dot-molecular beacon (QD-MB) probe is described. Two QD-MB probes were designed using 585 and 650-nm emitting CdTe QDs which were covalently conjugated to MBs with different DNA oligonucleotide sequences by amide linkage and streptavidin–biotin binding, respectively. The hybridizations of QD-MB probes with different DNA targets were then monitored by CE, and results indicated that the two QD-MB probes specifically hybridized with their complementary DNA sequences, respectively. Target DNA identification was observed to have a high sensitivity of 16.2pg in CE. Furthermore, the simultaneous detection of dual single-base mutations in a given DNA oligonucleotide was successfully achieved in CE using above two QD-MB probes. This novel CE-assisted QD-MB biosensor offers a promising approach for simultaneous detection of multiple single-base mutations, and exhibits potential capability in the single nucleotide polymorphism (SNP) analysis and high-sensitivity DNA detection. [ABSTRACT FROM AUTHOR]

Abstract: Here a new method for high-sensitivity quantum dot (QD)-based fluorescence resonance energy transfer (FRET) bioanalysis was developed. In this method, capillary electrophoresis (CE) with fluorescence detection was applied. The FRET system consisted of water-soluble 532-nm emitting CdTe QDs donor and 632-nm emitting CdSe/ZnS QDs acceptor which were covalently conjugated with mouse IgG and goat anti-mouse IgG, respectively. The bio-affinity between antigen and antibody brought two kinds of QDs close enough to make the FRET happen between them. In the CE experiments, highly efficient separation of donor-acceptor immunocomplexes was obtained, and the process of FRET was monitored. Results showed that FRET efficiency obtained by CE (38.56–69.58%) improved substantially in comparison with that obtained by ensemble measurement (12.77–52.37%). The high efficient separation of donor-acceptor immunocomplexes and the possible conformation change of antigen and antibody, contributes to the lower analysis uncertainty (variance) and higher FRET efficiency obtained in CE and consequentially, this makes the analysis of FRET more sensitive. This novel CE-based technique can be easily extended to other FRET system based on QDs and may have potential application in the study of biomolecule conformation change. [Copyright &y& Elsevier]

For ionic current rectification (ICR) based sensing, nanopore functionalizations are mostly designed for directly binding target molecules to generate detectable signals from surface charge variation. However, this strategy is highly dependent on the charge difference between the captured molecules and surface functionalization layers, which will increase the nanopore design difficulty and subsequently limit the nanopore applicability. Another key challenge for ICR based sensing is the nanopore regenerability that is critical if online monitoring or repeated determination needs to be performed with one sensor. Though some types of nanopore regeneration have been realized on some specific targets or with harsh conditions, it is still highly favored to develop a regenerability using mild conditions for various targets. To address these two challenges, we developed a novel and universal sensing strategy for aptamer-functionalized nanopore that can be easily regenerated after each usage without any harsh conditions and independent of target molecule charge or size for ICR based nanopore sensing. Ochratoxin A (OTA) was used as a model analyte and its corresponding aptamer partially hybridized with the pre-immobilized complementary DNA (cDNA) onto the nanopore inner surface. We demonstrated that the recognition and conjugation of OTA with its aptamer resulted in rectified ionic current variations due to the dissociation between the OTA aptamer and its partially paired cDNA. The performance of this nanopore sensor including sensitivity, selectivity, regenerability, and applicability was characterized using rectified ionic current. This nanopore sensing strategy will provide a promising platform for extensive targets and online sensing applications. • An ICR based nanopore sensing which performance is not limited by target molecule charge or size was successfully developed. • A nanopore regenerability that needs no harsh conditions or tedious steps was successfully realized. • The performance of this nanopore sensing was confirmed using Ochratoxin A as a model analyte. [ABSTRACT FROM AUTHOR]