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Open AccessLetter

Microfluidic Production of Autofluorescent BSA Hydrogel Microspheres and Their Sequential Trapping for Fluorescence-Based On-Chip Permanganate Sensing

by 1,2, 1,3,4,*, 2, 1,5 and 1,6,*
1
John A. Paulson School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
2
Jiangsu Key Laboratory for Design and Manufacture of Micro-Nano Biomedical Instruments, School of Mechanical Engineering, Southeast University, Nanjing 211189, China
3
State Key Laboratory of Rare Earth Resource Utilization, Changchun Institute of Applied Chemistry, Changchun 130022, China
4
State Key Laboratory of Rare Earth Resource Utilization, University of Science and Technology of China, Hefei 230026, China
5
Institute of Process Equipment, College of Energy Engineering, Zhejiang University, Hangzhou 310027, China
6
Center for Functional Sensor & Actuator (CFSN), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
*
Authors to whom correspondence should be addressed.
Sensors 2020, 20(20), 5886;
Received: 26 August 2020 / Revised: 15 October 2020 / Accepted: 15 October 2020 / Published: 17 October 2020
(This article belongs to the Special Issue Micro and Nanosensors for Biomedical)
Microfabrication technologies have extensively advanced over the past decades, realizing a variety of well-designed compact devices for material synthesis, separation, analysis, monitoring, sensing, and so on. The performance of such devices has been undoubtedly improved, while it is still challenging to build up a platform by rationally combining multiple processes toward practical demands which become more diverse and complicated. Here, we present a simple and effective microfluidic system to produce and immobilize a well-defined functional material for on-chip permanganate (MnO4) sensing. A droplet-based microfluidic approach that can continuously produce monodispersed droplets in a water-in-oil system is employed to prepare highly uniform microspheres (average size: 102 μm, coefficient of variation: 3.7%) composed of bovine serum albumin (BSA) hydrogel with autofluorescence properties in the presence of glutaraldehyde (GA). Each BSA hydrogel microsphere is subsequently immobilized in a microchannel with a hydrodynamic trapping structure to serve as an independent fluorescence unit. Various anions such as Cl, NO3, PO43−, Br, BrO3, ClO4, SCN, HCO3, and MnO4 are individually flowed into the microchannel, resulting in significant fluorescence quenching only in the case of MnO4. Linear correlation is confirmed at an MnO4 concentration from 20 to 80 μM, and a limit of detection is estimated to be 1.7 μM. Furthermore, we demonstrate the simultaneous immobilization of two kinds of different microspheres in parallel microchannels, pure BSA hydrogel microspheres and BSA hydrogel microspheres containing rhodamine B molecules, making it possible to acquire two fluorescence signals (green and yellow). The present microfluidics-based combined approach will be useful to record a fingerprint of complicated samples for sensing/identification purposes by flexibly designing the size and composition of the BSA hydrogel microspheres, immobilizing them in a desired manner and obtaining a specific pattern. View Full-Text
Keywords: droplet-based microfluidics; hydrodynamic trapping; BSA microspheres; autofluorescence; on-chip sensing droplet-based microfluidics; hydrodynamic trapping; BSA microspheres; autofluorescence; on-chip sensing
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MDPI and ACS Style

Liu, L.; Li, G.; Xiang, N.; Huang, X.; Shiba, K. Microfluidic Production of Autofluorescent BSA Hydrogel Microspheres and Their Sequential Trapping for Fluorescence-Based On-Chip Permanganate Sensing. Sensors 2020, 20, 5886.

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