antidotes needed to neutralize the anticoagulant activity.This work developed a double ion-exchange reaction-based photoelectrochemical (PEC) immunoassay with the split-type detection mode for sensitive detection of prostate-specific antigen (PSA, used as a model). The nanocomposite of cadmium sulfide and nickel sulfide (CdS@NiS nanocomposite), as the photoactive material, was rapidly synthesized by two-step hydrothermal treatment. In the presence of target PSA, the cupric oxide nanoparticle (CuO NP) labeled detection antibody was introduced into the detection system by sandwich immunoreaction and the copper (Cu2+) ions was released from CuO nanoparticles by acid to participate in double ion-exchange reaction. The double ion-exchange reaction on the photoelectric sensing interface between Cu2+ and CdS@NiS nanocomposites formed the weak photoactive material CuxS (x = 1, 2) to reduce the photocurrent. Under optimal conditions, the double ion-exchange reaction-based PEC immunoassay exhibited good photocurrent responses toward target PSA within the dynamic working range from 0.01 ng mL-1 to 50 ng mL-1 at a low limit of detection (LOD) of 2.9 pg mL-1. Besides, our work could achieve good reproducibility and high specificity under the split-type detection mode. Compared with human PSA ELISA kit, the accuracy obtained by our strategy was satisfactory. Importantly, this Cu2+-activated double ion-exchange reaction-based PEC immunoassay provides a promising platform for the detection of biomarkers.Hexavalent chromium ion (Cr6+) is highly toxic to human health and environment. Herein, high-performance detection of Cr6+ is of great import. In this study, a rapid and sensitive multicolor colorimetric method for detection of Cr6+ in aqueous solution was established on the basis of Cr6+ etching of gold nano-double cone@silver nanorods (Au NDC@Ag NRs). Au NDC@Ag NRs was synthesized by a modified seed-mediated growth method. The catalytic etching induced by Cr6+ changed the morphology of Au NDC@Ag NRs, leading to the attenuation of surface plasma resonance (SPR) and the redshift of absorption spectra. Meanwhile, Au NDC@Ag NRs exhibits obvious color changes from orange to pink, to purple, and finally becomes colorless with the increasing concentrations of Cr6+. With such a design, naked-eye detection of Cr6+ was realized with high sensitivity. The proposed multicolor sensing method showed a good linearity between the redshift change of absorption peak (△λ) and the concentrations of Cr6+ in the range from 2.5 to 40 μM. The limit of detection (LOD) was calculated as 1.69 μM in aqueous solution. In addition, successful detection of Cr6+ in tap water and Yangtze River water, indicating the real applications of Au NDC@Ag NRs probe in monitoring Cr6+ in environment.Recently, there has been significant interest in the influences of the human gut microbiota on many diseases, such as cardiovascular disease (CVD) and metabolic disorders. Trimethylamine N-oxide (TMAO) is one of the most frequently discussed gut-derived metabolites. CDK inhibitor drugs Dried blood spot (DBS) sampling has been regarded as an attractive alternative sampling strategy for clinical studies and offers many advantages. For DBS sample processing, whole-spot analysis could minimize hematocrit-related bias, but it requires blood volume calibration. This study developed a method combining matrix-induced ion suppression (MIIS) with liquid chromatography-electrospray ionization-tandem mass spectrometry (LC-ESI-MS/MS) to estimate blood volume and quantify TMAO and its precursors and derivatives, including choline, carnitine and acetylcarnitine, in DBSs. The MIIS method used an ion suppression indicator (ISI) to measure the extent of ion suppression caused by the blood matrix, which was related to the blood volume. The results showed that the volume estimation accuracy of the MIIS method was within 91.7-109.7%. The combined MIIS and LC-MS/MS method for quantifying TMAO, choline, carnitine and acetylcarnitine was validated in terms of linearity, precision and accuracy. The quantification accuracy was within 91.2-113.2% (with LLOQ less then 119%), and the imprecision was below 8.0% for all analytes. A stability study showed that the analytes in DBSs were stable at all evaluated temperatures for at least 30 days. The validated method was applied to quantify DBS samples (n = 56). Successful application of the new method demonstrated the potential of this method for real-world DBS samples and to facilitate our understanding of the gut microbiota in human health.Droplet microfluidics technologies have advanced rapidly, but enrichment in droplets has still been difficult. To deterministically control the droplet enrichment, the water transport from an aqueous microdroplet in organic continuous phase containing span 80 micelles was investigated. Organic phase containing Span-80-micelles contacted a NaCl aqueous solution to control hydration degree of the micelles, prior to being used in the microfluidic device. Then, the organic phase was continuously applied to the microdroplets trappled in microwells. Here, water was transported from the microdroplet to the organic phase micelles. This spontaneous emulsification process induced the droplet shrinkage and stopped when the microdroplet reached a certain diameter. The micelle hydration degree correlated well with the final water activity of droplets. The enrichment factor can be determined by the initial microdroplet salt concentration and by the micelle hydration degree. As a proof-of-concept experiment, enrichment of fluorescent nanoparticles and dye was demonstrated, and fluorescent resonance energy transfer was observed as expected. Another demonstration of bound-free separation was performed utilizing the avidin-biotin system. This technique has the potential to be a powerful pretreatment method for bioassays in droplet microfluidics.We proposed a simple and sensitive strategy for the detection of microRNAs (miRNAs) by converting homogeneous assay into surface-tethered electrochemical analysis. Specifically, the biotinylated detection probes (biotin-DNA-biotin) can trigger the in-situ assembly of tetrameric streptavidin (SA) proteins on an electrode surface via the SA-biotin interactions. The (SA-biotin-DNA-biotin)n assemblies electrically insulated the electrode interface, thereby blocking the electron transfer of [Fe(CN)6]3-/4-. When the probe was hybridized with the target miRNA, it would be cleaved into small fragments (denoted as biotin-DNA) by duplex-specific nuclease (DSN). The released target miRNA can enter into the next hybridization-enzymolysis cycle, thus leading to the generation of considerable amounts of biotin-DNA fragments. The released biotin-DNA competed with the detection probe to bind SA, thus limiting the in-situ formation of (SA-biotin-DNA-biotin)n assemblies. The surface-tethered electrochemical analysis by the dual signal amplification of DSN and (SA-biotin-DNA-biotin)n assemblies has been used for the determination of miRNAs in cell lysate with a satisfactory result.