Antibiotic exposure can cause the development of antibiotic resistant bacteria and can induce allergic reactions in humans. A source of high antibiotic exposure is contaminated dairy milk. To prevent contaminated dairy milk, development of antibiotic biosensors for on-site detection is required. This is particularly important for dairy farmers as fines and suspension of license are consequences of shipping contaminated milk to processing plants, where antibiotic tests are currently performed. There are also environmental and economic consequences when whole dairy tanks are contaminated and go to waste. Our work addresses this problem by developing an antibiotic biosensor for farmers to test their milk on-site for ciprofloxacin prior to sending to processing plants. Ciprofloxacin is frequently used to treat common bacterial infections in cattle. Our work provides the following contributions. We introduce an antibiotic biosensor that integrates fluorescence spectroscopy, microfluidic processing, and lock-in amplification to improve the limit-of-detection of ciprofloxacin below the regulatory limit for milk. We also perform traditional fluorescence detection for comparison. Our antibiotic biosensor has a signal-flow starting with an ultraviolet light emitting diode for illumination of ciprofloxacin, and moving through a microfluidic platform, a photodiode for detection of the fluorescent wavelength, and a lock-in amplifier. Our antibiotic biosensor is well-suited for fast on-site analyses and is designed for ease-of-use. Overall, our work shows promise for the integration of real-time on-site antibiotic detection of antibiotics in dairy.
Microfluidic technologies and on-chip optical components have advanced such that on-chip sensing of minute chemical and molecular compounds is possible, e.g., detection of gases, pathogens, and DNA. Such DNA analyses require purification and amplification to maximize sensitivity. A common method for amplification of a DNA segment is polymerase chain reaction (PCR), which amplifies DNA segments through temperature changes in an assay process. As such, there is great interest in optofluidic lab-on-a-chip PCR methods. However, developments are limited due to challenges in optically driven temperature fluctuations. These challenges arise when the microfluidic samples are smaller than the optical penetration depth of the incident light and only minimal absorption is achieved. To overcome these challenges, this work presents a bio-photonic approach to the PCR method which utilizes infrared (IR) radiation with whispering gallery mode (WGM) waves. The WGM waves greatly increase the interaction length in the microdroplet, allowing smaller (and scalable) dimensions. This improved interaction length occurs because the applied IR radiation is confined along the perimeter of the microdroplet and its surrounding medium. The operation is modelled with finite-different time-domain electromagnetic simulations, comparing current optical heating with the presented technique. These simulations are validated through an experimental analysis with a thermal camera measuring temperature fluctuations. Ultimately, the presented approach is shown to greatly increase scalability in PCR lab-on-a-chip systems.
Advancements in continuous and digital microfluidics (DMF) for integrated optics technologies are improving the feasibility of biophotonic sensors within lab-on-a-chip devices. Lab-on-a-chip diagnostic devices are achieving unprecedented high levels of throughput. Digital microfluidics, with its reconfigurable nature, is often utilized over continuous microfluidic systems due to reagent economy, precision, potential for scalability, and independent fluid actuation. However, scalability within DMF systems is currently inhibited by the DMF sensing architectures that are presently used, being capacitance and resistance sensing. These electrical-based sensing architectures probe each microdroplet location and this is difficult to scale. In this work, a fibre-optic sensing architecture is developed to improve scalability and achieve independent sensing of microdroplets. The sensing architecture utilizes an m × n (column and row) perpendicular overlap grid structure of embedded fibre-optic cables that yields m × n sensing positions with m + n measurement points. To evaluate both localized and practical scalability of the system, actuation contact time and differentiation of multiple microdroplets are assessed. The embedded fibre-optic cables will distribute light proportional to the number of microdroplets in contact along the column or row. Differentiation of multiple microdroplets is assessed with a theoretical model and through experimental measurements. The DMF sensing architecture is demonstrated for a three by three grid with multiple microdroplets present. The results show compatibility with high-speed DMF operation (due to fast contact times) and demonstrate scalable sensing of multiple microdroplets.
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