Label-Free Monitoring of Microorganisms and Their Responses to Antibiotics Based on Self-Powered Microbead Sensors

Rapid detection of bacteria and their susceptibility to specific antibiotics plays a vital role in microbial infection treatments. Antimicrobial susceptibility testing (AST) is a common measure to select effective drugs. However, the conventional practices, such as broth dilution, E-test, and disk diffusion, in clinical applications require a long turnaround time (-3 days), thereby compromising treatments and increasing mortality. This study presents self-powered sensors for on-site microorganism monitoring and rapid AST based on functionalized microbeads. The microbead sensors are driven by Brownian motion, rendering external power unnecessary. Fluorescent microbeads (d_p = 2 μm) were coated with vancomycin to capture bacteria. The growth and responses of Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus under antibiotic treatment were evaluated. The method showed stable selective binding despite the presence of some interferential substances, such as proteins and cells. Diffusivity change was strongly related to bacterial concentration. Accordingly, the diffusivity values of microbeads bound with motile and nonmotile bacteria exhibited specific patterns because of extra motility from microbes and increased particle diameter. Only a drop of microbead-bacteria suspension (-5 μL) was needed in a microchip for each measurement. The microchip provided a steady environment for measurement over a few hours. By distinguishing the slope of the last four data points in the temporal diffusivity curve, bacterial susceptibility or resistance to specific antibiotics could be determined within a time frame of 2 h. The study provides insights into saving more lives by using a fast and robust AST technique in future clinical practice.