A compact sample-to-answer system for rapid MRSA detection in serum based on reagent-free electrophoretic purification of nucleic acids and colorimetric LAMP

Methicillin-resistant <i>Staphylococcus aureus</i> (MRSA) poses a significant threat as a leading cause of nosocomial infections, inflicting severe complications and fatalities worldwide. Its rising prevalence has become a major public health concern as its resistance to common antibiotics complicates treatments, placing additional burden on healthcare systems. Microbial culture is the "gold standard" for diagnosing MRSA; however, this method is time-consuming and labor-intensive, often leading to prolonged delays in diagnosis and treatment. In contrast, nucleic acid amplification tests (NAATs) dramatically reduce diagnostic times to mere hours, while maintaining high sensitivity and specificity. Bringing NAATs to the point of care can facilitate timely treatment decisions and yet requires a compact "sample-to-answer" system whose development has long been hindered by the required sample preparation for these tests. Here, we present such a system detecting MRSA in human serum through a simple microfluidic chip, achieving a limit of detection of 1 CFU per reaction and a turnaround time of just 45 min. The chip effectively overcomes the sample preparation challenge with an innovative use of a sieve, a dense array of micropillars with submicrometer gaps. Along with associated reservoirs, this sieve integrates bacterial lysis, reagent-free electrophoretic purification and loop-mediated isothermal amplification (LAMP) of nucleic acids with colorimetric detection visible to the naked eye. Within the sieve, nucleic acids are selectively driven by rotating electric fields and focused near the sieve center while steady electric fields remove all contaminants, without the need for reagents. The system shows great potential for point-of-care diagnostics.