title: Universal quantum dot-based sandwich-like immunoassay strategy for rapid and ultrasensitive detection of small molecules using portable and reusable optofluidic nano-biosensing platform.
abstract: A universal sandwich-like immunoassay strategy based on quantum-dots immunoprobe (QD-labeled anti-mouse IgG antibody) was developed for rapid and ultrasensitive detection of small molecules. A portable and reusable optofluidic nano-biosensing platform was applied to investigate the sandwich-like immunoassay mechanism and format of small molecules, as well as the binding kinetics between QD immunoprobe and anti-small molecule antibody. A two-step immunoassay method that involves pre-incubation mixture of different concentration of small molecule and anti-small molecule antibody, and subsequent introduction of QD immunoprobe into the optofluidic cell was conducted for small molecule determination. Compared with the one-step immunoassay method, the two-step immunoassay method can obtain higher fluorescence signal and higher sensitivity index, thus improving the nano-biosensing performance. Based on the proposed strategy, two mode targets, namely, microcystin-LR (MC-LR) and Bisphenol A (BPA) were tested with high sensitivity, rapidity, and ease of use. A higher concentration of small molecules in the sample led to less anti-small molecule antibody bound with antigen-carrier protein conjugate immobilized onto the sensor surface, and less QD immunoprobes bound with anti-small molecule antibody. This phenomenon lowered the fluorescence signal detected by nano-biosensing platform. Under optimal operating conditions, MC-LR and BPA exhibited a limit of detection of 0.003 and 0.04 μg/L, respectively. The LODs were better than those of the indirect competitive immunoassay method for small molecules via Cy5.5-labeled anti-small molecule antibody. The proposed QD-based sandwich-like immunoassay strategy was evaluated in spiked water samples, and showed good recovery, precision and accuracy without complicated sample pretreatments. All these results demonstrate that the new detection strategy could be readily applied to the other trace small molecules in real water samples.
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China.
authors.forename: Liping
authors.initials: L
authors.lastname: Zhou
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China.
authors.forename: Anna
authors.initials: A
authors.lastname: Zhu
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China.
authors.forename: Xuening
authors.initials: X
authors.lastname: Lou
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China.
authors.forename: Dan
authors.initials: D
authors.lastname: Song
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Yang
authors.affiliation: School of Environment, Tsinghua University, Beijing, China.
authors.forename: Hanchang
authors.initials: H
authors.lastname: Shi
authors.affiliation: School of Environment and Natural Resources, Renmin University of China, Beijing, China. Electronic address: longf04@ruc.edu.cn.
authors.forename: Feng
authors.initials: F
authors.lastname: Long
mesh_terms: D015374:Biosensing Techniques; D007118:Immunoassay / Q000379:methods*; D057230:Limit of Detection; D044085:Microfluidics; D045663:Quantum Dots
keywords: Immunoassay; Nanosensor; Optofluidics; Quantum dots; Small molecule