A label-free fluorescence biosensor for highly sensitive detection of lectin based on carboxymethyl chitosan-quantum dots and gold nanoparticles

In this work, we report a novel label-free fluorescence turn off-on biosensor for lectin detection. The highly sensitive and selective sensing system is based on the integration of carboxymethyl chitosan (CM-CHIT), CuInS2 quantum dots (QDs) and Au nanoparticles (NPs). Firstly, CuInS2 QDs featuring carboxyl groups were directly synthesized via a hydrothermal synthesis method. Then, the carboxyl groups on the CuInS2 QDs surface were interacted with the amino groups (-NH2), carboxyl groups (-COOH) and hydroxyl groups (-OH) within CM-CHIT polymeric chains via electrostatic interactions and hydrogen bonding to form CM-CHIT-QDs assemblies. Introduction of Au NPs could quench the fluorescence of CM-CHIT- QDs through electron and energy transfer. In the presence of lectin, lectin could bind exclusively with CM-CHIT-QDs by means of specific multivalent carbohydrate-protein interaction. Thus, the electron and energy transfer process between CM-CHIT-QDs and Au NPs was inhibited, and as a result, the fluorescence of CM-CHIT-QDs was effectively turned on. Under the optimum conditions, there was a good linear relationship between the fluorescence intensity ratio I/I-0 (I and I-0 were the fluorescence intensity of CM-CHIT-QDs-Au NPs in the presence and absence of lectin, respectively) and lectin concentration in the range of 0.2-192.5 nmol L-1, And the detection limit could be down to 0.08 nmol L-1. Furthermore, the proposed biosensor was employed for the determination of lectin in fetal bovine serum samples with satisfactory results. (C) 2016 Elsevier B.V. All rights reserved.