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Colorimetric assay platforms for dissolved hydrogen sulfide (H2S) have been developed for more than 100 years, but most still suffer from relatively low sensitivity. One promising route out of this predicament relies on the design of efficient signal amplification methods. Herein, we rationally designed an unprecedented H2S-induced deactivation of (gold core)@(ultrathin platinum shell) nanocatalysts (Au@TPt-NCs) as a highly efficient signal amplification method for ultrasensitive headspace-colorimetric assay of dissolved H2S. Upon target introduction, Au@TPt-NCs were deactivated to different degrees dependent on H2S levels, and the degrees could be indicated by using a Au@TPt-NCs-triggered catalytic system as a signal amplifier, thus paving a way for H2S sensing. The combination of experimental studies and density functional theory (DFT) studies revealed that the Au@TPt-NCs with only 2-monolayer equivalents of Pt (θPt = 2) were superior for H2S-induced nanocatalyst deactivation owing to their enhanced peroxidase-like catalytic activity and deactivation efficiency stemmed from the unique synergistic structural/electronic effects between Au nanocores and ultrathin Pt nanoshells. Importantly, our analytical results showed that the designed method was indeed highly sensitive for sensing H2S with a wide linear range of 10-100 nM, a slope of 0.013 in the regression equation, and a low detection limit of 7.5 nM. Also the selectivity, reproducibility, and precision were excellent. Furthermore, the method was validated for the analysis of H2S-spiked real samples, and the recovery in all cases was 91.6-106.7%. With the merits of high sensitivity and selectivity, simplification, low cost, and visual readout with the naked eye, the colorimetric method has the potential to be utilized as an effective detection kit for point-of-care testing. [ABSTRACT FROM AUTHOR]

Photoelectrochemical (PEC) detection is an emerging and promising analytical tool. However, its actual application still faces some challenges like potential damage of biomolecules (caused by itself system) and intrinsic low-throughput detection. To solve the problems, herein we design a novel split-type photoelectrochemical immunoassay (STPIA) for ultrasensitive detection of prostate specific antigen (PSA). Initially, the immunoreaction was performed on a microplate using a secondary antibody/primer-circular DNA-labeled gold nanoparticle as the detection tag. Then, numerously repeated oligonucleotide sequences with many biotin moieties were in situ synthesized on the nanogold tag via RCA reaction. The formed biotin concatamers acted as a powerful scaffold to bind with avidin-alkaline phosphatase (ALP) conjugates and construct a nanoenzyme reactor. By this means, enzymatic hydrolysate (ascorbic acid) was generated to capture the photogenerated holes in the CdS quantum dot-sensitized TiO2 nanotube arrays, resulting in amplification of the photocurrent signal. To elaborate, the microplate-based immunoassay and the high-throughput detection system, a semiautomatic detection cell (installed with a three-electrode system), was employed. Under optimal conditions, the photocurrent increased with the increasing PSA concentration in a dynamic working range from 0.001 to 3 ng mL-1, with a low detection limit (LOD) of 0.32 pg mL-1. Meanwhile, the developed split-type photoelectrochemical immunoassay exhibited high specificity and acceptable accuracy for analysis of human serum specimens in comparison with referenced electrochemiluminescence immunoassay method. Importantly, the system was not only suitable for the sandwich-type immunoassay mode, but also utilized for the detection of small molecules (e.g., aflatoxin B1) with a competitive-type assay format. [ABSTRACT FROM AUTHOR]