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A split-type and dual-mode (photoelectrochemical and electrochemical, PEC and EC) biosensor was developed for non-invasive and sensitive detection of cortisol in saliva, based on antibody-aptamer sandwich model and enzyme catalytic amplification. Platinum nanoparticles (PtNPs)/CdIn4S2/TiO2/FTO served as the sensing electrode, and glucose oxidase/aptamer-conjugated Au nanoparticles (GOx-AuNPs-Apt) served as the measurement probe. In the presence of the target cortisol, a sandwich complex including cortisol, antibody, and GOx-AuNPs-Apt detection probe could be formed. When glucose and 4-chloro-1-naphthol (4-CN) were present, GOx and AuNPs in the complex worked together to catalyze glucose to generate H2O2, which encouraged PtNPs to catalyze 4-chloro-1-naphthol to generate a significant amount of benzo-4-chlorohexadienone (4-CD) precipitation. However, in the absence of cortisol, there was no 4-CD precipitation because none of the above catalytic reactions could be carried out. As an effective quencher, 4-CD may reduce photocurrent while simultaneously increasing charge transfer resistance, so a double-signal immunosensor using 4-CD as the signal indication was built. With the increase of target concentration, the PEC signal decreased while the EC signal increased, and within optimal conditions, this sensor had a good linear relationship in the range of 0.001−1000 ng/mL. The detection limits of photochemistry and electrochemistry were 0.8 pg/mL and 0.4 pg/mL, respectively. Furthermore, the designed method had acceptable recoveries of 88.0–114.7% and well-matched accuracy using the commercialized human cortisol ELISA kit and standard HPLC-MS as references. Photoelectrochemical and electrochemical dual-mode biosensor for salivary cortisol: Integrating antibody-aptamer sandwich pattern with enzyme catalytic amplification [ABSTRACT FROM AUTHOR]

Abstract: A new flow-through electrochemical aptasensor was designed for ultrasensitive monitoring of adenosine triphosphate (ATP) by coupling microvalve-programmable capillary column with CdS-functionalized DNA concatamer for signal amplification. Initially, a layer of primary DNA-conjugated polyacrylamide hydrogel was covalently linked onto the internal surface of capillary column, and then an automated sequenctial injection format with a syringe pump was employed for development of the programmable capillary-based aptasensor. In the presence of target DNA aptamer, the immobilized primary DNA hybridized with partial bases of the aptamer. The excess aptamer fregment could trigger the formation of DNA concatamer between auxiliary DNA1 and CdS-labeled auxiliary DNA2. Upon target ATP introduction, a specific ATP-aptamer reaction was excuated, thereby resulting in the release of CdS-functionalized DNA concatamer from the capillary. Subsenquent anodic stripping voltammetric detection of cadmium released under acidic conditions from the released CdS nanoparticles could be conducted in a homemade detection cell. Under optimal conditions, the dynamic concentration range spanned from 0.1pM to 10nM ATP with a detection limit of 0.06pM ATP. The electrochemical aptasensor showed good reproducibility, selectivity, and stability. In addition, the methodology was evaluated for the analysis of ATP spiked serum samples, and the recoveries was 81–140%. [Copyright &y& Elsevier]

We report on a new electrochemical biosensing strategy for the sensitive detection of hydrogen peroxide (HO) in foodstuff samples. It is based on a gold electrode modified with layer of graphene patterned with a multilayer made from an organic-inorganic hybrid nanomaterial. Initially, a layer of thionine (Th) was assembled on the surface of the graphene nanosheets, and these were then cast on the surface of the electrode for the alternate assembly of gold nanoparticles and horseradish peroxidase. The large surface-to-volume ratio and high conductivity of the nanosheets provides a benign microenvironment for the construction of the biosensor. The use of such a multilayer not only shortens the electron transfer pathway of the active center of the enzyme due to the presence of gold nanoparticles, but also enhances the electrocatalytic efficiency of the biosensor toward the reduction of HO. The electrochemical characteristics of the biosensor were studied by cyclic voltammetry and chronoamperometry. The number of layers, the operating potential, and the pH of the supporting electrolyte were optimized. Linear response is obtained for the range from 0.5 μM to 1.8 mM of HO, the detection limit is 10 nM (at S/N = 3), and 95% of the steady-state current is reached within 2 s. The method was applied to sense HO in spiked sterilized milk and correlated excellently with the permanganate titration method. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

A photoelectrochemical (PEC) sensor is proposed with a TiO 2 /CdIn 2 S 4 co-sensitive structure and a g-C 3 N 4 -WO 3 heterojunction as the photoanode to form a self-powered system. The photogenerated hole-induced biological redox cycle of TiO 2 /CdIn 2 S 4 /g-C 3 N 4 -WO 3 composites is used as a signal amplification strategy for Hg2+ detection. In the test solution, ascorbic acid is first oxidized by the photogenerated hole of the TiO 2 /CdIn 2 S 4 /g-C 3 N 4 -WO 3 photoanode, which triggers the ascorbic acid－glutathione cycle to achieve signal amplification and increase the photocurrent. However, in the presence of Hg2+, glutathione forms a complex with Hg2+, which destroys the biological cycle and leads to a decreased of photocurrent, thus achieving detection of Hg2+. Under optimal conditions, the proposed PEC sensor has a wider range (from 0.1 pM to 100 nM), and lower limit of Hg2+ detection (0.44 fM) than most other Hg2+ detection methods. In addition, the developed PEC sensor can be used to detect of real samples. This study successfully developed a self-powered photoelectrochemical sensor coupling with biological redox cycling amplification for quantitative detection of Hg2+ by using TiO 2 /CdIn 2 S 4 / g-C 3 N 4 -WO 3 photoanode. [Display omitted] • A self-powered photoelectrochemical sensor is proposed for mercury ion detection. • A biological redox cycle is used for the first time as a signal amplification strategy. • TiO 2 /CdIn 2 S 4 /g-C 3 N 4 -WO 3 is used as photoanode materials for the first time. [ABSTRACT FROM AUTHOR]