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

•A label-free near-infrared fluorescence “turn off-on” biosensor for detection of lectin was established.•The highly sensitive biosensor was based on the inner filter effect of Au NPs on CM-CHIT-QDs.•Lectin could bind exclusively to CM-CHIT-QDs via multivalent carbohydrate-protein interactions, and “turn on” the fluorescence.•The biosensor sensor showed good selectivity for the detection of lectin with a low detection limit of 0.07 nM.

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/I0 (I and I0 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.

Graphical abstractA label-free fluorescence biosensor for highly sensitive detection of lectin based on the integration of carboxymethyl chitosan, CuInS2 quantum dots and gold nanoparticles.Figure optionsDownload full-size imageDownload as PowerPoint slide