Ultrasmall metal nanoclusters are attractive for their size-dependent optical and electrochemical properties. Here, blue-emitting copper clusters stabilized with cetyltrimethylammonium bromide (CTAB) are synthesized using an electrochemical approach. The electrospray ionization (ESI) analysis reveals that the cluster has 13 copper atoms in the core. The clusters are then used for the electrochemical detection of endotoxina bacterial toxin in Gram-negative bacteria. Differential pulse voltammetry (DPV) is used to detect endotoxins with high selectivity and sensitivity. It shows a lower detection limit of 100 ag mL–1 with a linear range of 100 ag mL–1 to 10 ng mL–1. The sensor is efficient for detecting endotoxins from human blood serum samples.

Endotoxins or lipopolysaccharides (LPS) present in the outer layer of Gram-negative bacteria (GNB) are responsible for bacterial toxicity. It is an environmental hazard that everyone is exposed to daily to various extents. Due to its potent toxicity, quantitative detection with very high sensitivity is essential in the food, medical, and pharmaceutical industries. Herein, we report an optical nanosensor for the rapid and sensitive detection of LPS and GNB based on the Cu2+-mediated aggregation of gold nanoparticles (Cu@AuNPs). The sensor detects LPS within a linear range of 20 ag/mL to 20 ng/mL with a lower detection limit of 0.2 ag/mL. The sensor could successfully recover spiked endotoxin in grape juice with a percentage error of ±0.2, confirming its application in the food industry. The sensor could also distinguish Gram-negative bacteria from Gram-positive bacteria, and the selectivity of the Cu@AuNP sensor toward GNB is utilized to detect Escherichia coli in wastewater. The rapid detection of E. coli without any pretreatment is a promising strategy in water analysis.

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