Exploiting pH-Regulated Dimer-Tetramer Transformation of Concanavalin A to Develop Colorimetric Biosensing of Bacteria

Abstract

Gold nanoparticles (AuNPs) aggregation-based colorimetric biosensing remains a challenge for bacteria due to their large size. Here we propose a novel colorimetric biosensor for rapid detection of Escherichia coli O157:H7 (E. coli O157:H7) in milk samples based on pH-regulated transformation of dimer/tetramer of Concanavalin A (Con A) and the Con A-glycosyl recognition. Briefly, antibody-modified magnetic nanoparticles was used to capture and concentrate E. coli O157:H7 and then to label with Con A; pH adjusted to 5 was then applied to dissociate Con A tetramer to release dimer, which was collected and re-formed tetramer at pH of 7 to cause the aggregation of dextran-modified AuNPs. The interesting pH-dependent conformation-transformation behavior of Con A innovated the design of the release from the bacteria surface and then the reconstruction of Con A. Therefore, we realized the sensitive colorimetric biosensing of bacteria, which are much larger than AuNPs that is generally not suitable for this kind of method. The proposed biosensor exhibited a limit of detection down to 41 CFU/mL, short assay time (~95 min) and satisfactory specificity. The biosensor also worked well for the detection in milk sample, and may provide a universal concept for the design of colorimetric biosensors for bacteria and virus.

Oxidative Bio-Desulfurization by Nanostructured Peroxidase Mediator System

“…The activity yield of HRP was found to be dependent on the specific nature of LNPs in the absence of polyelectrolyte. Cat I showed an activity yield significantly lower than cat II (Table 1, entry 1 versus entry 2), suggesting that the different hydrophobicity and elemental composition of OL with respect to KL was a relevant parameter in tuning the efficacy of the Con A immobilization, probably due to dissociation of its dimeric sub-units [51]. This hypothesis is in accordance with the reported hydrophilicity character of Con A layers [52].…”

Lignin nanoparticles are renewable and functional platforms for the concanavalin a oriented immobilization of glucose oxidase–peroxidase in cascade bio-sensing

“…In the rst case (pathway A), Con A from jack beans (Canavalia ensiformis) was adsorbed on the surface of LNPs by treating the nanoparticles (1.5 mg mL À1 ) in sodium phosphate buffer (PBS, 1.0 mL; pH 7.3, 0.1 M) with different concentration of Con A (from 0.2 mg mL À1 to 1.0 mg mL À1 ) in the same buffer (1.0 mL) at 25 C. The tetrameric conguration of Con A necessary for the molecular recognition of glycoproteins was preserved by buffering the pH of the system (pH 7.3). 48 The efficacy of the adsorption of Con A was evaluated by the Bradford assay on the residual solution aer removal of the nanoparticles. 49 The interaction between lectins and polyphenols is reported, mainly focusing on their relevance for nutraceutical aspects.…”

Rapid naked-eye detection of Gram-positive bacteria by vancomycin-based nano-aggregation

“…27,28 Rapid sensing technologies utilizing uorescence, magnetic, or colorimetric detection have been introduced as novel approaches as diagnostic assays for various disease targets. [29][30][31][32][33][34][35][36][37][38][39][40] Among these, a colorimetric detection method allowing nakedeye detection would be advantageous and easily applicable as a bedside assay in point-of-care settings. Detection based on molecularly induced aggregation have been usefully applied since they can be designed as a simple assay involving a onestep, wash-free procedure.…”

“…29,30 Aggregation-based assays using gold nanoparticles have been one of the most widely studied, and have been applied for diagnosing diseases such as cancer and infectious diseases. [31][32][33][34][35][36] For bacteria, studies based on the aggregation of gold nanoparticles utilizing concanavalin A, 34 cell wall peptide subunits, 35 and boronic acid derivatives 36 were reported, however could not distinguish various types of Grampositive pathogens from Gram-negative bacteria. Another method using platinum-coated magnetic nanoparticle clusters for immunoseparation and colorimetric detection has been reported, however a washing step was required and also allowed the detection of a single type of pathogen.…”