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The discrimination of structurally similar biothiols remains a critical challenge in clinical diagnostics, as conventional nanozyme-based sensor arrays often suffer from limited signal diversity and poor discriminative ability. To address this, a colorimetric sensor array using two rationally designed chiral carbon dots (CDs) was constructed. The role of chirality was primarily reflected in regulating the catalytic heterogeneity and enriching the multi-channel response diversity rather than direct enantioselective recognition. The two chiral CDs possess markedly distinct oxidase-like and laccase-like activities. This disparity in catalytic activity effectively doubles the number of response channels, thereby enriching the cross-reactive signal patterns. The CDs catalyzed the oxidation of three chromogenic substrates, namely 3,3',5,5'-tetramethylbenzidine (TMB), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and the 4-aminoantipyrine/2,4-dichlorophenol (4-AP/2,4-DP) coupling system in the absence of H₂O₂, producing distinct colorimetric responses. The addition of thiols elicits a differential inhibition of this activity in a degree-dependent manner, thereby inducing characteristic changes in the colorimetric readout. The developed array enabled accurate simultaneous identification and quantitative analysis of four thiols, including glutathione (GSH), L-cysteine (Cys), homocysteine (Hcy), and thioglycolic acid (TGA), by extracting RGB values using a smartphone color picker app and combining them with principal component analysis (PCA), hierarchical cluster analysis (HCA), and supervised machine learning. The k-nearest neighbor (KNN), support vector machine (SVM), and random forest (RF) classifiers achieved overall classification accuracies ranging from 95.83% to 97.22%, which further confirmed the robustness and reliability of the proposed sensing strategy. PCA score plots showed well-separated clusters for all analytes over the concentration range of 1-100 μM, while HCA further confirmed 100% classification accuracy. Furthermore, the first principal component (PC1) exhibited good linear correlation with GSH and TGA concentrations in a wide linear range of 1-50 μM, and the detection limit for all thiols was 1 μM. Successful application in serum and urine samples highlights its potential for smartphone-based clinical disease diagnosis.

Developing a low-cost, highly sensitive, and accurate fluorescence-based approach for Cu²⁺ detection is crucial for reducing heavy metal pollution in industrial effluent. Here, we report a newly synthesized Schiff base europium metal-organic framework (Eu-MOF) and demonstrate its use for turn-off fluorescent detection of Cu²⁺. A Schiff base ligand derived from 2-aminoterephthalic acid and 2-hydroxynicotinaldehyde was coordinated with Eu³⁺ to construct the framework, enabling a simple and rapid sample pretreatment procedure. The material exhibited pH-dependent fluorescence behavior. With the concentration range of 2.5 to 500 mg L^-1, a linear response to Cu²⁺ was observed. The limit of quantification (LOQ) was 2.5 mg L^-1, while the limit of detection (LOD) was 0.83 mg L^-1. The method was effectively performed on vinegar, tea, fruit juice, and water samples, yielding spike recoveries of 84.5%-100.9% and relative standard deviations (RSDs) of 1.7%-4.8%. This method can be used to determine Cu²⁺ in various matrices.

Endotoxin detection is critical for the diagnosis and management of sepsis and for the safety evaluation of pharmaceutical products. Here, we report a peptide-based digital enzyme-linked immunosorbent assay (dELISA) that integrates two high-affinity, phage-displayed peptides into a single-molecule array platform, enabling highly sensitive and specific endotoxin detection without the use of antibodies. The carboxylated activation of magnetic beads was optimized using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) at 10 °C, and L-lysine (Lys) was identified as an effective blocking agent that maintained bead monodispersity through electrostatic repulsion. Under optimized conditions, the assay achieved a detection limit of 0.2 pg mL^-1 with a linear range spanning 0-200 pg mL^-1. The method exhibited strong accuracy (coefficient of variation (CV) < 15%) and interference resistance (recovery rates of 76.9%-110.1%) when applied to pharmaceutical formulations such as saline, 5% dextrose, and commercial ophthalmic solutions. In clinical validation, the platform successfully quantified endotoxin in plasma samples from septic and non-septic patients and demonstrated excellent recovery (78.0%) in whole blood spiked with exogenous endotoxin. By eliminating antibody-related limitations, this peptide-based dELISA offers a robust and translational tool for direct endotoxin detection in complex biological matrices.