Department of Chemistry and Biochemistry, National Chung Cheng University, Chia-Yi 621, Taiwan.
Center for Nano Bio-Detection, Advanced Institute of Manufacturing with High-tech Innovations (AIM-HI), National Chung Cheng University, Chia-Yi 621, Taiwan.
Sensors (Basel). 2020 Dec 15;20(24):7177. 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.
当含有表面增强拉曼散射（SERS）标记结合细菌（本研究中为沙门氏菌）的 100 μL 离心富集样品被虹吸到靠近嵌入式热电加热芯片的玻璃载玻片上时，这样的固定液滴会迅速蒸发。由于在加热过程中样品液滴的尺寸显著减小，来自驻留在样品上方的 corona 放电针的离子风会扫过液体表面，产生离心涡旋流。标记结合的沙门氏菌随后被拖曳并捕获在液滴底部的中心。最后，当样品干燥时，与“咖啡环”效应不同，SERS 标记结合的沙门氏菌集中在一个小斑点中，以允许对拉曼信号进行灵敏检测。与我们之前仅包含 corona 放电针的电动力学浓缩装置相比，这种热电蒸发辅助装置更省时，浓缩和干燥约 100 μL 样品的时间从 2 小时缩短至 30 分钟。因此，该装置可以加速样品通量，以便实际应用。它也更灵敏，能够实现对纯样品中少数沙门氏菌细胞的 SERS 检测。我们还评估了该装置在不进行培养程序的情况下检测食品样品中沙门氏菌的可行性。将少量沙门氏菌细胞掺入冰块和生菜叶中，我们使用过滤和超速离心步骤获得 200 μL 富集的标记结合沙门氏菌样品。将 100 μL 样品的等分试样加载到该浓缩装置上后，可以成功检测到含有两个沙门氏菌细胞的 100 g 冰块和含有 5 个沙门氏菌细胞的 20 g 生菜叶样品的 SERS 标记信号。
