Micro-PAD card for measuring total ammonia nitrogen in saliva.

This work presents a portable microfluidic paper-based analytical device (micro-PAD) card for the quantification of total ammonia nitrogen in human saliva. The amount of total ammonia nitrogen in saliva can be an indicator of the status of the oral microbiome with potential correlation to kidney health problems. The developed micro-PAD card comprises twenty units consisting of three stacked layers of circular discs: the sample layer, paper discs impregnated with sodium hydroxide solution, the PTFE membrane layer, and the detection layer, paper discs impregnated with bromothymol blue. The twenty units were aligned on transparent laminating pouches laminated to form the micro-PAD card (7.5 cm × 10.5 cm). Saliva samples can be directly dispensed onto the micro-PAD card and the detection was achieved by the BTB indicator color change, from yellow to blue, after conversion of ammonium into ammonia and diffusion of the ammonia gas through a hydrophobic layer. The determination of total ammonia nitrogen in saliva using the developed micro-PAD card intended to be very simple method and operated without the need of laboratory equipment. A quantification limit of 11.3 NH4+mg L-1 and linear application range from up to 150 NH4+mg L-1 were obtained making it suitable for the expected concentrations of total ammonia nitrogen in human saliva. It was successfully applied to saliva samples and its validation obtained by comparison against a potentiometric method. The card is stable for at least 1 month making it ideal as a portable device for point-of-care diagnosis. Graphical Abstract.

Tuberculosis Diagnosis Using Isothermal Nucleic Acid Amplification in a Paper-and-Plastic Device.

Nucleic acid (DNA/RNA) amplification technologies are indispensable for applications like disease diagnostics, forensics, epidemiology, evolutionary biology, vaccine development, and therapeutics. While polymerase chain reaction (PCR) has deeply penetrated the abovementioned fields and has been commercially successful, two major common disadvantages are exorbitant costs of associated equipment, which create concerning roadblocks in terms of affordability and accessibility. This work describes development of an inexpensive, portable, easy-to-use and deliverable-to-end-users, nucleic acid amplification technology for infectious disease diagnosis. The device uses loop-mediated isothermal amplification (LAMP) and cell phone-based fluorescence imaging to enable nucleic acid amplification and detection. A regular lab incubator and a custom-made low-cost imaging box are the only two additional equipment required for testing. Material cost for a 12-test zone device was $0.88, and cost of reagents per reaction was $0.43. First successful application of the device was demonstrated for tuberculosis diagnosis with clinical sensitivity of 100% and clinical specificity of 68.75% for testing of 30 clinical patient samples.

Nanoparticle-based Point of Care Immunoassays for in vitro Biomedical Diagnostics.

In resource-limited settings, the availability of medical practitioners and early diagnostic facilities are inadequate relative to the population size and disease burden. To address cost and delayed time issues in diagnostics, strip-based immunoassays, e.g. dipstick, lateral flow assay (LFA) and microfluidic paper-based analytical devices (microPADs), have emerged as promising alternatives to conventional diagnostic approaches. These assays rely on chromogenic agents to detect disease biomarkers. However, limited specificity and sensitivity have motivated scientists to improve the efficiency of these assays by conjugating chromogenic agents with nanoparticles for enhanced qualitative and quantitative output. Various nanomaterials, which include metallic, magnetic and luminescent nanoparticles, are being used in the fabrication of biosensors to detect and quantify biomolecules and disease biomarkers. This review discusses some of the principles and applications of such nanoparticle-based point of care biosensors in biomedical diagnosis.

A paper-based length of stain analytical device for naked eye (readout-free) detection of cystic fibrosis.

The test of sweat chloride is routinely performed as a worldwide newborn screening (NBS) to the diagnosis of cystic fibrosis (CF) in infants. However, the available methods for measurement of chloride in sweat suffer from such limitations as either low selectivity and/or requiring relatively large sample size. In this work, we have designed an analytical ruler that can measure chloride ion in sweat and hence can be used for the diagnosis of cystic fibrosis. This micro-pad (µ-PAD) device is fabricated by making hydrophilic micro-channel on a filter paper impregnated with silver dichromate. After addition of chloride ion-containing sweat sample, it moves through the channel, leading to the formation of an AgCl sediment, which deposits as a white color stain, the length of which in the channel being proportional to the amount of chloride ion in sweat. A well-defined linear relation was observed between the length of white color stain and the concentration of chloride ion in the sample solutions with a relative standard deviation of 3.6% (n = 3) for an artificial sweat sample containing 100 mM chloride ion. The possible interfering effects of several different cations and anions on the detection of chloride ion were investigated and the results well-confirmed the selectivity of the proposed method. With the use of only 2.0 µL of the sample solution, the µPAD was able to measure the chloride content of sweat over a concentration range of 20.0-100.0 mM, which covers both the healthy range (˂ 40 mM) and the risky range (˃60 mM) of chloride ion. Analysis of chloride content of sweat samples by the µPAD agreed well with those obtained by a standard electrochemical method (with relative errors of lower than 10%).