Salmonella ser. Typhimurium is notorious for causing serious foodborne illnesses and presenting considerable public health risks. The study introduces an innovative system based on a quartz crystal microbalance, designed to detect the target pathogen by integrating the system around a smartphone. The system operates through a dual-mode approach, relying on two distinct mechanisms: measuring frequency changes due to variations in bacterial mass and quantifying fluorescence intensities resulting from bacteria captured by FITC-labeled antibodies. Incorporating FITC-labeled antibodies not only enhances the resonance frequency shift but also offers visual confirmation through the fluorescence signal. The integration of the quartz crystal microbalance system with a smartphone enables real-time monitoring. This system displays both frequency and temperature data, while also capturing fluorescence intensities to estimate the concentration of the target analyte. The smartphone-based system successfully detected Salmonella Typhimurium within a concentration range of 105 CFU/mL after the application of FITC-labeled antibodies. This portable QCM system represents a promising advancement in pathogen detection, holding significant potential to improve food safety protocols and strengthen public health safeguards.
Recently, the use of a Quartz Crystal Microbalance (QCM) as a biosensor for detecting foodborne pathogens by observing changes in resonant frequency has gained popularity. However, conventional detection methods are time-consuming and require expensive equipment and trained personnel. The current trend is toward detection approaches that are quick, portable, and easy to use. In order to address this need, a dual-modality QCM system combining a smartphone, an in-situ fluorescence imaging subsystem, and a flow injection component has been proposed. This system enables a smartphone to receive real-time frequency data via Bluetooth, while a camera detects the presence of bacteria on the quartz crystal surface using a fluorescence-tagged antibody. The fluorescence imaging subsystem utilizes a camera to capture the bacteria fluorescence signal, while the flow injection subsystem employs a mini peristaltic pump and controller to introduce biochemical solutions, antibodies, and bacteria. All components are contained in a 3D cartridge that is portable. FITC images were captured with 5 MHz quartz crystals when the prototype system was tested. The developed QCM biosensor has the potential to become a portable bacteria detection approach that outperforms existing techniques.
Infection with foodborne pathogens such as Salmonella spp. is of high risk for people with a weakened immune system. Microbiological culture method has been used in general for detection of pathogens from the food matrix; however, it is time consuming and requires experience and good level of laboratory skills. In the food safety field, various techniques which allows the rapid and simple detection have been developed at the level of a user-friendly tool for detecting the foodborne pathogens. Quartz crystal microbalance (QCM) are mass-based biosensor which measures the microgram level mass changes, enabling a user to observe the presence of the pathogen simply and rapidly. When the pathogens are bound on vibrating quartz surface, the resonant frequency of a quartz crystal will be changed due to the mass of the pathogens. In this study, the QCM detected killed Salmonella Typhimurium in the range of 〖10〗^5-〖10〗^9 CFU/mL, correlating to the averaged frequency shifts. The actual concentrations of Salmonella from the culture method were compared to the difference in the resonant frequency. The QCM sensor were treated with 11-Mercaptoundecanoic acid (11-MUDA), and EDC-NHS following by antibodies and bovine serum albumin (BSA) to utilize the antibody-antigen reaction. With a usage of peristaltic pump, the solutions could be introduced to the surface while frequencies could be monitored for each step in real-time. To acquire the evidence of Salmonella, the surfaces of the quartz crystal with the fluoresce labeled antibody were captured by the fluorescence microscope. The QCM biosensor showed the possibility of detection of Salmonella in less time, compared with the conventional method.
Quartz crystal microbalance (QCM) sensors have been applied to detect foodborne pathogens such as Salmonella Typhimurium, E.coli O157:H7, and Campylobacter jejuni. As pathogens are placed on vibrating quartz surface, the change in mass of the pathogens affects the characteristic of a QCM. The presence of pathogens that antibody captures can be correlated to the shift in resonance frequency. Thus, theoretical description is necessary to understand the relationship between the change in frequency and mass. In this work, the relationship between theoretical and experimental results is examined by comparing the frequency shift caused by different type of liquids. In general, a QCM can be represented by a Butterworth-Van-Dyke (BVD) circuit made up of resistance R, inductance L, and capacitance C. With physical properties of quartz, viscosity-density product of the liquid has an effect on inductance as well as resistance. As a preliminary experiment, measurements of mixtures of water and glycerol were conducted to evaluate results from the different levels of viscosity and density. The results of the experiments showed that higher viscosity and density resulted in lower resonant frequencies. With regard to theoretical calculation, increase of R and L resulted in a proportional increase in the square root of the viscosity-density product. Increased lumped parameters explains the decreased resonant frequency. Therefore, the shift of the resonant frequency of the load and unloaded QCM could be calculated based on the admittance from circuit components. Blank (air) sample, water, glycerol and water mixture have shown proportional shift in the resonant frequencies. The experiments and theoretical model were matched within reasonable range. The average difference between the theory and the experiments (Matlab/FEM model) was 7.04 %.
Luminescence based detection has been widely used in diverse science and engineering applications. The recent development of the smartphone has enabled end users to utilize this communication device as a portable detector and instruments such as a microscope, fluorimeter, colorimeter, and spectrometer. To transform the smartphone into a bioluminescence detector, our group developed an advanced signal processing algorithm and an optical chamber designed for efficient photon capture. This solution was required to overcome the typical sensitivity of the CMOS-based smartphone camera such that sub-nano to pico Watt levels of power can be measured with conventional smartphones. Preliminary experiments conducted with the bioluminescent Pseudomonas fluorescens M3A shows a detection limit of approximately 106 CFU/ml. To achieve sensitive detection while maintaining the portability, we explored using the recently developed silicon photomultiplier (SiPM), and designed a portable bioluminescence sensor which shows a 2-3 order higher sensitivity on calibration sample testing. Finally, for live sample testing, Escherichia coli O157:H7 was inoculated on a ground beef sample and subjected to luminescence phage based detection and a luminescence signal was generated from the bacteriophage infection and detected within 8-10 h after spiking.
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