Contamination detection often requires lengthy culturing steps to detect low-level bioburden. To increase the rate of detection and decrease the limit of detection (LOD), a system featuring microfluidics and a multichannel fluorometer has been developed. The 8-channel fluorometer enables parallel testing of multiple samples with LOD as low as < 1 CFU/mL. This low-cost system utilizes the slope of fluorescence intensity that serves as the criterion for bioburden detection. The redox indicator dye resazurin is used to monitor the presence of viable cells, in this study and is reduced to resorufin with a high quantum yield at 585 nm. The sample under investigation is spiked with resazurin, loaded in a special-design microfluidic cassette and the rate of change is observed via the fluorometer. The method was validated using primary E. coli culture in comparison with a spectrophotometer which served as the gold standard. An optimized assay based on LB media was developed. The impact on the assay sensitivity based on incubation and filtration steps was also explored. The assay is shown to pick up inadvertent contamination from test tubes and pipette tips showing its applicability in real-world settings. The data analysis demonstrated a comparable performance of the multichannel fluorometer vis-a-vis the conventional plate reader. The multichannel system is shown to detect bioburden presence in as low as 20 seconds for bacterial concentrations ≥ 5 CFU/mL after 6 hours of incubation. Considering its portability, low cost, simplicity of operation and relevant assay sensitivity, the system is well-positioned to detect low-level bioburden in the laboratory, pharmaceutical and field settings.
There is an increasing interest in low-cost, facile and versatile thermoplastic bonding for microfluidic applications that can be easily transitioned from laboratory prototyping to industrial manufacturing. In addition, owing to the surge in the usage of thermoplastic microfluidics and its adverse effect on the environment, it is prudent to source alternative materials that are biodegradable, providing a sustainable, green approach. To address the problems, here we introduce an environment friendly, low-cost and safe welding technology used in the fabrication of microcassettes from biodegradable cellulose acetate (CA) thermoplastics. The thermally assisted solvent based bonding of the thermoplastics was accomplished in a domestic microwave oven with the aid of a polyether ether ketone (PEEK) vise. To characterize the quality of the bonding, our in-house technique was compared with a conventional thermally assisted solvent bonding configuration using a heat press machine and tested under different conditions. Our microwave induced bonding of CA presents three times reduced bonding time with higher bonding strength, good reliability and does not necessitate the use of cumbersome instrumentation. Finally, we demonstrate an electrophoresis application and vitamin C detection accomplished using this biodegradable microcassette presenting comparable results with traditional techniques, illustrating the potential of this fabrication technique in different microfluidic applications.
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