We have amplified an 84 bp fragment from the insertion sequence IS6110 of Mycobacterium tuberculosis (MTB) DNA on a paper substrate in 10 min. Tuberculosis (TB) is a highly infectious disease with a high mortality rate in the developing countries. Cheap and rapid screening assays are needed at the point of care for timely intervention and treatment. While PCR-based detection of TB is faster than bacterial culture and more specific compared to microscopy, PCR is not viable as a routine screening test in many low-income countries where TB is endemic due to the requirement of an expensive thermocycler. Disease screening based on isothermal amplification techniques is, therefore, being explored as an alternative to PCR. Successful isothermal amplification of DNA from HIV, H1N1, Chlamydia trachomatis, E. coli, etc. on cheap and disposable paper substrates has been reported in the literature. Isothermal amplification of MTB DNA on paper has been challenging due to the high GC content (65%) of MTB genome. Here we report helicase dependent amplification of a fragment of MTB DNA on a paper substrate in 10 min starting from 100 copies of the template using inexpensive heat sources, such as hot plates and hand warmers. The enzyme mix used to amplify DNA can be spotted and stored dry on paper at ambient temperatures for more than a month. The DNA amplified on paper can be detected by incorporating a suitable fluorescence marker in the reaction mixture or by directly loading the paper in a standard gel electrophoresis set up. Finally, as a surrogate to real clinical sputum samples, MTB DNA was successfully amplified on paper in the viscous environment of artificial sputum.

This paper reports for the first time printed-circuit-board (PCB)-based label-free electrochemical detection of bacteria. The demonstrated immunosensor was implemented on a PCB sensing platform which was designed and fabricated in a standard PCB manufacturing facility. Bacteria were directly captured on the PCB sensing surface using a specific, pre-immobilized antibody. Electrochemical impedance spectra (EIS) were recorded and used to extract the charge transfer resistance (R_ct) value for the different bacteria concentrations under investigation. As a proof-of-concept, Streptococcus mutans (S. mutans) bacteria were quantified in a phosphate buffered saline (PBS) buffer, achieving a limit of detection of 10³ CFU/mL. Therefore, the proposed biosensor is an attractive candidate for the development of a simple and robust point-of-care diagnostic platform for bacteria identification, exhibiting good sensitivity, high selectivity, and excellent reproducibility.

We developed a two-layer microfluidic device to study the motility dynamics of E. coli. We show that both confinement and chemoattractant lead to anomalous diffusion, with power-law distributed run lengths and suppression of large-angle tumbles.

Detection of bacterial colonies in water is a pressing issue in recent times owing to its implications on human health, leading to an urgent need for low cost, disposable sensors. In this work, we report a disposable impedimetric sensor for detection of total bacterial colonies present in water samples. The sensor consists of a polyaniline coated filter paper functionalized with a homo-bi functional crosslinker, glutaraldehyde. Prior to the functionalization step, two Ag electrodes are deposited on the filter paper using conductive silver paste. The aldehyde groups of glutaraldehyde bind with the amine functional groups present on bacterial cell wall resulting in a change in dielectric constant, and consequently, the capacitive effect between the two Ag electrodes. Also, bacterial metabolism affects the medium conductivity and in turn, the medium resistance changes. The combined effect of changes in capacitive effect as well as resistance is reflected as a change in AC impedance measured using a frequency response analyzer (FRA). E. coli and Pseudomonas aeruginosa bacteria are detected in PBS buffer up ∼ to 500 cfu/mL. Testing is also carried out by spiking tap water and grey water with known concentrations of bacteria samples. The detection limits obtained are 500 – 1000 cfu/mL with a response time of ∼ 20 minutes. The developed sensor provides rapid, moderately sensitive, costeffective solution for detecting total bacterial load in water samples.