Integration of a Thermoelectric Heating Unit with Ionic Wind-Induced Droplet Centrifugation Chip to Develop Miniaturized Concentration Device for Rapid Determination of Salmonella on Food Samples Using Antibody-Functionalized SERS Tags

• Published in: Sensors (Basel, Switzerland) Vol. 20; no. 24; p. 7177
• Main Authors: Chen, Yi-Jhen, Chen, Yuan-Yu, Wang, Kai-Hao, Wang, Chih-Hsien, Yang, Chiou-Ying, Chau, Lai-Kwan, Wang, Shau-Chun
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 15-12-2020; MDPI
• Subjects: Antibodies; Bacteria; bacteria detection; Centrifugation; Cubes; Droplets; Electrohydrodynamics; Filtration; Food Analysis - instrumentation; Food Analysis - methods; Food Microbiology; Food safety; Heating; ionic wind; Liquid surfaces; Methods; microcentrifuge; microfluidics; Nanoparticles; Pathogens; Raman spectra; Salmonella; SERS tag; Spectrum Analysis, Raman; thermoelectric drying; Thermoelectricity; Wind effects; SERS tag; ionic wind; bacteria detection; thermoelectric drying; food sample; microfluidics; microcentrifuge
• ISSN: 1424-8220; 1424-8220
• DOI: 10.3390/s20247177

When a centrifugation-enriched sample of 100 μL containing the surface-enhanced Raman scattering (SERS) tag-bound bacteria (Salmonella in this study) is siphoned onto a glass slide next to an embedded thermoelectric heating chip, such a sessile droplet is quickly evaporated. As the size of the sample droplet is significantly reduced during the heating process, ionic wind streams from a corona discharge needle, stationed above the sample, sweep across the liquid surface to produce centrifugal vortex flow. Tag-bound Salmonella in the sample are then dragged and trapped at the center of droplet bottom. Finally, when the sample is dried, unlike the "coffee ring" effect, the SERS tag-bound Salmonella is concentrated in one small spot to allow sensitive detection of a Raman signal. Compared with our previous electrohydrodynamic concentration device containing only a corona discharge needle, this thermoelectric evaporation-assisted device is more time-effective, with the time of concentrating and drying about 100 μL sample reduced from 2 h to 30 min. Hence, sample throughput can be accelerated with this device for practical use. It is also more sensitive, with SERS detection of a few cells of Salmonella in neat samples achievable. We also evaluated the feasibility of using this device to detect Salmonella in food samples without performing the culturing procedures. Having spiked a few Salmonella cells into ice cubes and lettuce leaves, we use filtration and ultracentrifugation steps to obtain enriched tag-bound Salmonella samples of 200 μL. After loading an aliquot of 100 μL of sample onto this concentration device, the SERS tag signals from samples of 100 g ice cubes containing two Salmonella cells and 20 g lettuce leaf containing 5 Salmonella cells can be successfully detected.