Layer-by-Layer Assembly of Polycations and Polyanions for the Sensitive Detection of Endotoxin.

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.

Highly sensitive endotoxin detection using a gold nanoparticle loaded layered molybdenum disulfide-polyacrylic acid nanocomposite.

Endotoxins or lipopolysaccharides (LPS) are pathogens released from the outer membrane of gram-negative bacteria which produce toxic effects on humans. The sensitive and selective detection of LPS is in high demand, especially in the field of medical supplies, therapeutics and in the food industry. Herein we report a new nano-probe based on a gold nanoparticle loaded, water-soluble layered molybdenum disulfide-polyacrylic acid (Au/MoS2-PAA) nanocomposite as a label-free voltammetric aptasensor for ultrasensitive LPS detection. MoS2 nanosheets were obtained through one-step sonication assisted exfoliation of bulk MoS2 with polyacrylic acid (PAA). Au nanoparticles were incorporated into the MoS2-PAA nanocomposite and thiol terminated LPS binding aptamers (LBA) were immobilized on this. The specific binding of LPS with LBA is investigated electrochemically by differential pulse voltammetry. The apparent binding constant (Kb) of LPS with LBA has been calculated to be 1.53 × 102 mL g-1. The aptasensor demonstrated LPS detection down to the ag mL-1 level without incorporating any redox mediator and showed wide linearity from 100 ag mL-1 to 100 pg mL-1 with a low limit of detection of 29 ag mL-1. The sensor showed excellent recovery upon spiking LPS in clinical grade insulin, suggesting that LBA/Au/MoS2-PAA/GCE has promising application for the trace analysis of LPS in the field of pharmaceutical products.

1-Pyrene carboxylic acid functionalized carbon nanotube-gold nanoparticle nanocomposite for electrochemical sensing of dopamine and uric acid.

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.

Gold atomic cluster mediated electrochemical aptasensor for the detection of lipopolysaccharide.

We have constructed an aptamer immobilized gold atomic cluster mediated, ultrasensitive electrochemical biosensor (Apt/AuAC/Au) for LPS detection without any additional signal amplification strategy. The aptamer self-assemble onto the gold atomic clusters makes Apt/AuAC/Au an excellent platform for the LPS detection. Differential pulse voltammetry and EIS were used for the quantitative LPS detection. The Apt/AuAC/Au sensor offers an ultrasensitive and selective detection of LPS down to 7.94 × 10-21M level with a wide dynamic range from 0.01 attomolar to 1pM. The sensor exhibited excellent selectivity and stability. The real sample analysis was performed by spiking the diluted insulin sample with various concentration of LPS and obtained recovery within 2% error value. The sensor is found to be more sensitive than most of the literature reports. The simple and easy way of construction of this sensor provides an efficient and promising detection of an even trace amount of LPS.