Microfluidics for Microbiology: Point-of-care Pathogen Detection

Periodic pandemic and epidemic disease outbreaks due to deadly microbial pathogens, lead to millions of deaths worldwide and pose a significant challenge to public health, world of work, food systems, economic and social status. For control and prevention of infectious diseases, timely and accurate prognosis and disease diagnosis is of utmost importance. Further, rapid and accurate detection of microbial pathogens and identification of their multidrug resistant (MDR) strains is of primary clinical significance for disease control and to shorten the course of drug regimen during therapy [1]. Clinical diagnostic laboratories most often use traditional methods such as microbial culture, nucleic acid-based tests, enzyme linked immune sorbent assays (ELISA), however, these are time consuming and require expensive equipment, tedious protocol and laboratory trained personnel. These limitations of traditional microbiological methods present a bottleneck for resource-limited facilities and remote areas sample testing [2]. According to the World Health Organization (WHO), there remains an unprecedented global need for novel diagnostic technologies with affordability, specificity, sensitivity, ease of use, robustness, short response time and deliverability to end-users.             To overcome the limitations of traditional methods used in clinical diagnostic microbiology, a rapid, cost-effective, portable system integrated with microfluidic devices were developed for pathogen detection [3]. To provide an efficient platform for both sample preparation and quantitative and qualitative detection, microfluidic systems are made of fast, integrated, miniaturized features, which are coupled with conventional optical or electrochemical devices [6]. Microfluidic chip contains engraved or molded patterns of microchannels, where each microchannel is a flow passage with hydraulic diameter of 10-200 µm [2-4]. This network of microchannels within the microfluidic chip is linked to the macro environment by hollowing out several holes of various dimensions through the chip [3]. In order to achieve automation, multiplexing and high-throughput screening, the fluids may be directed, separated, mixed or manipulated [3]. These fluids are injected into or evacuated from the microfluidic chip through the holes. The microchannels network is designed with precision to attain the desired features such as detection of pathogens, DNA analysis, lab-on-a-chip, electrophoresis etc [3]. With advancement in material science, different materials e.g. silicon, glass, quartz/ fused silica, metals, soft or hard polymers, ceramics are used for fabrication of networks in microfluidic system to perform diverse functions [2-3]. Detection and quantification of pathogens using microfluidic system eliminates the need for cell culture. This integrated system also allows analysis of effect of treatment by active compounds/ drugs, as well as the study of interactions between cells and drug carriers [3]. Microfluidic chips are coupled with various conventional macro-scale analytical systems such as electrochemical sensors, optical biosensors, mass spectrometers, magneto-resistive sensors (GMR) to develop ultra-sensitive platforms for detection of microbial pathogens and specific real-time biochemical analysis [3]. Microbial pathogens such as Pseudomonas aeruginosa (P. aeruginosa), Salmonella typhimurium (S. typhimurium), Escherichia coli (E. coli) O157:H7, Enterococcus faecium (E. faecium), Staphylococcus aureus (S. aureus), Vibrio vulnificus (V. vulnificus), and Stenotrophomonas maltophilia (S. maltophilia), Streptococcus, Legionella pneumophila, Salmonella, Shigella were detected within 10-15 minutes using microfluidic system integrated with optical analyzer [1-7]. Combining nano-dielectrophoretic enrichment-based microfluidic platform with surface-enhanced Raman scattering (SERS), E. coli O157:H7 was automatically monitored in drinking water [5]. Multiple clinical pneumonia-related pathogens were detected within 45 minutes using air-insulated microfluidic chip [6]. Identification of Mycoplasma pneumoniae (M. pneumoniae), S. aureus and methicillin-resistant S. aureus from sputum samples of 229 patients was achieved using a portable nucleic acid analyser, which was integrated with mechanical, confocal optical, electronic, and software functions to detect highly sensitive fluorescence signal [7]. Several microfluidic systems were designed for detection of viral pathogens such as HIV, ZIKA, Hepatitis B [8]. Pathogen detection based on microfluidic chips facilitate easy sample preparation, amplification and accurate signal detection, thereby reducing the time for generation of results and making detection system more cost-effective, rapid, sensitive and specific. The high throughput efficiency of microfluidic system is suitable for resource-limited facilities/areas and point-of-care testing of broad range of pathogens [1-8]. Fig. 1 is the schematic representation for detection of microbial pathogens using microfluidic system integrated with reverse transcription loop-mediated isothermal amplification (RT-LAMP).             This review aims to provide fundamentals on microfluidic platform for detection of microbial pathogens. It also includes advances and advantages of analytical technologies integrated with microfluidics and the challenges in the development of portable devices. This review can serve as the basic foundation for future research to develop point of care testing devices for rapid and accurate detection of deadly microbial pathogens using microfluidic chips.