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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.

Bacterial contamination is a serious concern for health and environmental safety. The major toxic effect arises from the endotoxin or lipopolysaccharide (LPS) attached to the cell wall of the gram-negative bacteria. Ultrasensitive endotoxin detection is of supreme importance in sustaining food, clinical and pharmaceutical safety. Herein we report a simple electrochemical detection platform using reduced graphene oxide (rGO) combined with cuprous oxide nanoparticles for the ultrasensitive detection of LPS. The sensor uses polymyxin B (PmB) to achieve the selective response towards LPS. The sensor showed a lower detection limit (LOD) of 10 agmL -1 with linearity from 10 agmL -1 to 10 ngmL -1 . Detection of LPS from whole blood is also carried out with excellent sensitivity. The sensor showed excellent recovery rates in whole blood, pointing to the capability of using the sensor in real-life clinical analysis. The sensor detects Gram-negative bacteria from sewage water with a rapid response time, indicating the effectiveness of the sensor in water quality analysis., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

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 Cu 2+ -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.

Bacterial endotoxin detection is an essential safety requisite in biomedical, food, and pharmaceutical industries. Endotoxin in a sufficient concentration on entering the human bloodstream causes detrimental effects such as septic shock, which can lead to death. Hence, the sensitive and selective detection of endotoxin also known as lipopolysaccharide (LPS) is of paramount importance. Herein, a layer-by-layer (LBL) assembly of gold-chitosan nanocomposite (CGNC)-poly(acrylic acid) (PAA)-polymyxin B (PmB) on gold (Au) electrode is employed for the sensitive and selective detection of endotoxin. The surface electric charge studies using dynamic contact mode electrostatic force microscopy (DC-EFM) revealed the successful formation of each layer on the Au electrode. The polycationic PmB is a specific bioreceptor of LPS, which binds with high affinity to the anionic groups of the carbohydrate portions of LPS molecules and facilitates the selective electrochemical detection. This surface modification method presented a sensitive and selective detection of endotoxin down to the attogram level.

A highly sensitive, selective and cost effective method is described for sensing dopamine (DA) and uric acid (UA). A glassy carbon electrode (GCE) was modified with a nanocomposite consisting of gold nanoparticle-loaded multi-walled carbon nanotube (CNT) modified with 1-pyrene carboxylic acid (PCA). The stable aqueous dispersion of non-covalently functionalized CNT-PCA is an efficient bioprobe for the ultra sensitive and selective detection of dopamine and uric acid in the presence of the potentially interfering agent ascorbic acid (AA). The presence of PCA on the CNT introduces anionic carboxyl groups which repel ascorbate. The presence of the pyrene group augments high electrocatalytic activity towards oxidation of DA and UA, and the gold nanoparticles contribute to the amplification of the signal. The modified GCE gives an excellent peak current with well distinguishable peaks for AA, DA and UA (near -0.08 V, +0.14 V, and +0.22 V vs Ag/AgCl) in differential pulse voltammetry. Chronoamperometric detection of DA (working potential of 0.16 V vs Ag/AgCl) and UA (working potential of 0.3 V vs Ag/AgCl) showed linear ranges of 1 nM-150 μM (LOD 1 nM) and 1 μM-240 μM (LOD 1 μM) for DA and UA, respectively. The nanoprobe was validated by monitoring the recovery of spiked DA and UA in human blood serum samples which indicated a recovery within ±2%. Graphical abstract A glassy carbon electrode modified with a gold nanoparticle-loaded multi-walled carbon nanotube (CNT) - 1-pyrene carboxylic acid (PCA) composite was used for the sensitive and selective detection of the dopamine and uric acid.