Plasmonic response of aptamer-functionalized gold nanoparticles via target-induced aggregation for oxytetracycline detection.

Split aptamer-regulated AuNF nanozymes for colorimetric and electrochemical dual-readout kanamycin biosensing.

Kanamycin (Kana) residues released into aquatic environments due to its extensive use have raised increasing concerns because of their potential risks to ecosystems and human health. In this work, we report a label-free split aptamer-modified gold nanoflower (AuNF)-based aptasensing platform with colorimetric and electrochemical readouts for the determination of Kana in water. Two thiolated split aptamer fragments (SPA1 and SPA2) were immobilized on AuNFs through Au-S bonds. The flower-like AuNFs provided a high-surface-area scaffold for aptamer loading, while the DNA modification further enhanced the peroxidase-like activity of AuNFs toward TMB oxidation. In the presence of Kana, target-induced assembly of SPA1 and SPA2 promoted the aggregation of AuNFs, which inhibited their catalytic activity toward TMB oxidation, thereby reducing oxTMB formation and the resulting colorimetric and electrochemical signals. Based on this signal-off mechanism, the platform enabled quantitative detection of Kana with linear ranges of 100-3000 nM for colorimetry and 50-2000 nM for chronoamperometry, with limits of detection of 0.51 and 0.074 nM, respectively. The method also showed satisfactory selectivity, reproducibility, and storage stability. In spiked environmental water samples, recoveries ranged from 87.7% to 106.2% with relative standard deviations below 5.0%, and the electrochemical results were in acceptable agreement with those obtained by HPLC-MS. This study provides a simple and effective dual-readout aptasensing strategy for Kana determination in environmental water samples.

Rapid Broad-Spectrum Colorimetric Detection of Bacteria Using Polylysine-Mediated Gold Nanoparticle Aggregation.

Rapid on-site detection of bacterial contamination remains an urgent need in public health and environmental monitoring. Herein, we report a one-step, label-free colorimetric sensor for broad-spectrum bacterial detection based on a competitive electrostatic mechanism. Cationic poly-l-lysine (PLL) induces the aggregation of anionic, citrate-capped gold nanoparticles (AuNPs), resulting in a distinct red-to-blue color change. In the presence of bacteria, their negatively charged surfaces adsorb PLL, thereby inhibiting AuNP aggregation and maintaining the red color of the dispersion. This strategy enables the visual detection of various Gram-positive and Gram-negative bacteria within 10 min. Using Escherichia coli (E. coli) as a model analyte, the assay reached a detection limit of 720 CFU/mL under the optimized conditions (5 μg/mL PLL, 3 min incubation, 20 mM phosphate buffer at pH 7.5) and exhibited a wide detection range from 102 to 107 CFU/mL (R2 > 0.99). The assay also performed reliably in spiked tap water and drinking water samples, with recoveries of 82-96% and CVs below 10%, demonstrating its potential as a rapid, low-cost screening tool for bacterial contamination in low-matrix water samples.

A fluorescent aptasensor based on the synergy of Au NPs/PDDA/LEG nanocomposite and CDs for aflatoxin B1 detection.

Aflatoxin B1 (AFB1), a potent carcinogen produced by Aspergillus fungi, contaminates foods such as corn and peanuts and thereby introduces a serious food safety risk, as it is known to cause liver damage and cancer. Therefore, developing sensitive and rapid detection methods is crucial for protecting public health. This work presented a highly sensitive aptasensor for AFB1 detection, utilizing a fluorescence quenching and recovery strategy based on a gold nanoparticles/poly (diallyldimethylammonium chloride)/liquid-phase exfoliation of graphene (Au NPs/PDDA/LEG) nanocomposite. The composite sensing platform was constructed by employing PDDA to enhance the dispersion of LEG and prevent the aggregation of Au NPs. Aptamers were immobilized onto the Au NP surface via Au-S bonds. Concurrently, carbon dots (CDs) were conjugated to complementary DNA (cDNA) to form cDNA/CDs. In the absence of AFB1, hybridization between the aptamer and cDNA brought CDs into close proximity with Au NPs, resulting in the quenching of CDs fluorescence due to the proximity to Au NPs. Upon the introduction of AFB1, its specific binding to the aptamer competitively displaced cDNA/CDs. This displacement separated CDs from the Au NPs, leading to the recovery of fluorescence intensity. Demonstrating excellent analytical performance, the sensor offered not only a wide linear detection range (1.0 × 10-2-1.0 × 103 ng mL-1), but also a remarkably low limit of detection (LOD) at 1.05 pg mL-1. Testing with corn and peanut samples yielded high recovery rates of 97.63% to 109.65%, confirming the method's reliability, accuracy, and significant potential for practical food safety monitoring of AFB1.

Core–shell Au@CeO2 nanozyme-mediated aptasensor for dual-mode SERS/colorimetric detection of kanamycin

Ultrasensitive aptasensor based on SERS-coupled immunochromatography for rapid detection of fenvalerate in food samples.

In this study, we developed an aptamer-mediated surface-enhanced Raman scattering (SERS)-coupled immunochromatographic assay (ICA) for the quantitative detection of pyrethroids. For this approach, core-shell gold nanoparticles (Au@Au NPs) were used as SERS probes by conjugating with aptamers, and fluorescent Raman reporter molecules (MPBN) were incorporated to yield stable, reproducible spectral signals. Leveraging the aptamers' specific recognition of the target analyte, Raman-labeled Au@Au NPs could be effectively captured by the test line of the immunochromatographic strip, thereby enabling the quantitative analysis of fenvalerate-with a limit of detection (LOD) as low as 0.4 ppb. Comparative experiments revealed that the detection sensitivity of this SERS-ICA method was 476 times higher than that of conventional lateral flow assays (LFA), showcasing a remarkable sensitivity advantage. To validate its practicality, spiked recovery experiments were conducted on three real samples, namely welsh onions, cowpeas, and kidney beans. The results showed that the spiked recoveries ranged from 78.3% to 112.5%, with relative standard deviations (RSD) between 1.7% and 20.1%. This fully confirms that the method possesses favorable specificity and accuracy, making it suitable for real-sample detection. This detection platform offers a new technical route for the rapid on-site monitoring of trace contaminants in food safety and environmental surveillance, holding broad application prospects.

Aptamer-functionalized aggregation-induced emission micelles for integrated detection and photodegradation of lipopolysaccharides.