Smartphone-Integrated Optomechanical Dual-Mode Instrument for <i>Salmonella</i> Typhimurium Detection

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Salmonella</i> Typhimurium is responsible for numerous cases of foodborne illnesses, often resulting in severe hospitalizations and fatalities. The imperative to detect and prevent such foodborne pathogens is crucial for safeguarding public health. This research introduces the creation of a quartz-crystal microbalance system integrated with a smartphone, aiming to identify the presence of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Salmonella</i> Typhimurium through a dual-mode approach. This innovative system employs two distinct mechanisms: first, by gauging frequency changes induced by bacterial mass, and second, by quantifying fluorescence intensities arising from bacteria captured by fluorescein isothiocyanate (FITC)-labeled antibodies. The utilization of FITC-labeled antibodies impacts the measurement in two ways: it enhances the frequency-shift signal for mass change and facilitates the visualization of bacterial cells via optical detection. The integration of the smartphone with the quartz-crystal microbalance system enables the real-time presentation of frequency data and the recording of fluorescence intensities, allowing for the estimation of cell numbers. The smartphone-based system effectively detected <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Salmonella</i> Typhimurium within a concentration range of 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> to 10<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> CFU/mL following the application of FITC-labeled antibodies.