Magnetic nanochain enabled microarray and microfluidic bioassays

• Main Author: Xiong, Qirong
• Other Authors: Duan Hongwei
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Chemical engineering::Biochemical engineering
• Online Access: https://hdl.handle.net/10356/106491; http://hdl.handle.net/10220/47991
• Institution: Nanyang Technological University

There are growing demands for bioassay techniques that allow for rapid, multiplexed detection of a panel of targets with minimum specimen consumption. However, the devices of small size often present fundamental problems such as intrinsic poor liquid mixing and inefficient mass transfer across microfluidic channels and diffusion-limited on-surface assays, which create considerable obstacles to achieve rapid, ultrasensitive detection. Recently, we developed polydopamine (PDA) based strategy to produce one-dimensional (1-D) magnetic nanochains with rigid structure. The magnetic nanochains immediately align in a magnetic field and undergo synchronous rotation in response to a rotating magnetic field, making them ideal nanomixers to promote fast fluid mixing and analyte transport in microscale devices. Importantly, PDA not only serves as the scaffold to lock the nanochain structure, but also allows for convenient surface functionalization by means of spontaneous Michael addition and/or Schiff base reaction with nucleophilic thiol and amine groups. As such, the nanochains can be sequentially functionalized with specific antibody for target separation, thus realize multi-functional roles in bioassay. In the first system, we prepared dual-functional magnetic nanochains based on the facile polydopamine (PDA) strategy. In this study, the mixing and bioseparation behaviors of magnetic nanochains were thoroughly investigated by theoretical analysis and experimental observations. Our results demonstrated the magnetic nanochains immediately align in a magnetic field and undergo synchronous rotation in response to a rotating magnetic field at the maximum frequency of 540 rpm. In a microfluidic chamber, the mixing efficiency (σM) induced by magnetic nanochains can quickly reach to 80% within 1 min, making ideal nanomixer to promote fast fluid mixing and analyte transport in micro-scale assay devices. This, together with the readily functionalized surface, allows the magnetic nanochains to serve as both tiny stir bars for active liquid mixing and capture agents for targets of interest at high capture rate within 5 min. Microarray techniques have found widespread uses in diverse fields ranging from fundamental genomic research to clinical diagnosis. However, static assays in conventional microarray platforms give rise to slow turnaround time due to diffusion-limited reaction kinetics. In the second system, we used PEGylated magnetic nanochains to improve DNA and Protein microarray assay. The rotating magnetic nanochains in sample solutions serve as tiny stir bars to promote dynamic mixing and effectively accelerate the transportation of targets to the vicinity of the probes immobilized on glass surface. Our results have shown that the use of magnetic nanomixers led to improved kinetics, increased sensitivities, and reduced signal variation in both of DNA and protein microarray analysis. The magnetic dynamic nanomixers were expected to find widespread uses in on-surface bioassays that suffer from diffusion limitation, such as microfluidic assays, enzyme-linked immunosorbent assay (ELISA), and heterogeneous catalysis. Finally, we used this dual-functional magnetic nanochains in microfluidic bioassay. It is well-recognized that while microfluidic biochips hold great promise in liquid analysis for biomedical research and clinical diagnosis. However, the devices of this size scale often present fundamental problems such as intrinsic poor liquid mixing and inefficient mass transfer across microfluidic channels and diffusion-limited on-surface assays, which create considerable obstacles to achieve rapid, ultrasensitive detection. In this study, we report a new type of magnetic nanochains integrated biochip (MiChip). In our MiChip assay, bioconjugated nanochains are actuated by tailored magnetic fields to play dual-functional roles as nanoscale stir bars and capture/enrichment agents, promoting concerted active liquid mixing and bioseparation. The use of dual-functional magnetic nanochains integrates the key functions of microfluidic bioanalysis (i.e., liquid mixing, target bioseparation and signal transduction) into a streamlined process in a simple microfluidic system. In this study, we demonstrate that the MiChip assay allows rapid, parallel analysis of small volumes (~1 μl) of real clinical specimens. Cancer protein markers in serum samples from 20 cancer patients and specific bacteria in human saliva were sensitively and selectively quantified within 8 min.