Toward a Quantitative Colorimeter for Point-of-Care Nitrite Detection

Abstract

This paper reports on a low-cost, quantitative, point-of-care solution for the early detection of nitrite, a common biomarker for urinary tract infections (UTIs). In a healthy individual, nitrite is not found in the urine. However, a subject with a suspected UTI will produce nitrite in their urine since the bacteria present will convert nitrate into nitrite. Traditionally, nitrite is monitored by urinary dipsticks that are either read by eye or using a reflectance spectrophotometer. Both methods provide a semiquantitative positive or negative result at best. In this paper, we described a novel, affordable, portable transmission-based colorimeter for the quantitative measurement of nitrite. A unique permutation of the Griess reaction was optimized for the clinical detection of nitrite in urine and is reported. By using nitrite spiked in a salt buffer, artificial, and human urine samples, the performance of the colorimeter was evaluated against dipsticks read using two commercial dipstick analyzers, Urisys 1100 (Roche Diagnostics) and Clinitek Status+ (Siemens Medical Solutions). The colorimeter was able to detect the clinically relevant range of nitrite from 0.78 to 200 μM in a salt buffer. The detection limit in artificial urine was determined as 1.6 μM, which is ∼16× more sensitive than commercial dipstick reflectance analyzers, enabling the possibility for earlier detection of urinary infections. The colorimeter is assembled using off-the-shelf components (<$80) and controlled by a smartphone application via low-energy bluetooth. It has a built-in color correction algorithm and is designed to enable for a turbidity correction in samples containing bacteria or other cellular debris as well. The mobile application can display the nitrite concentration for a single sample or display the results over a period of time. Tracking urinalysis results longitudinally can help identify trends such as increases in nitrite concentrations over an individual’s baseline and identify possible infections earlier. While the detection of nitrite was showcased here, this portable analyzer can be expanded to other colorimetric-based chemistries to detect a panel of biomarkers, which can improve the overall sensitivity and specificity of the desired assay.

Current Status and Future Perspectives of Lactate Dehydrogenase Detection and Medical Implications: A Review

“…A colorimeter is a laboratory instrument that details the concentration represented by a color and is widely used for the routine measurement of substance concentrations because of advantages such as affordability, portability and direct visual observation of the results [ 64 , 96 , 97 ]. As shown in Figure 3 , Kannan et al developed a highly stable and mass-produced colorimetric biosensor for LDH detection, which can be operated in less than 5 min and has a detection limit as low as 13 U/L.…”

“…However, the colorimetric method can only be applied to samples with relatively simple composition that are less susceptible to interference. Moreover, its relatively low sensitivity is obstacle to its wide application [ 60 , 96 ].…”

Development of a Quantitative Digital Urinalysis Tool for Detection of Nitrite, Protein, Creatinine, and pH

“…Nitrite detection relied on the Griess reaction, consisting of an aniline derivative and a coupling reagent in an acidic solution. The p-arsanilic acid and NED combination proved to be the most sensitive and stable over at least 25 days [14]. A pink azo-dye product resulted from the Griess reaction, leading to maximum absorption in green wavelengths.…”

“…Nitrite detection used the optimized Griess reaction, as described in our previous single-channel colorimeter paper [14]. Briefly, a solution was prepared by adding 0.0325 g of p-arsanilic acid to 24.75 mL of distilled water and then combined with 0.25 mL of hydrochloric acid (37%).…”

“…Urine color can vary widely, and it can be influenced by factors such as dehydration, health status, and dietary choices. To address the potential impact of color and turbidity on analyte measurements, we developed correction algorithms detailed in [14]. To demonstrate the color measurement capability, five cuvettes each containing different colored dyes were prepared and inserted into the last channel of the colorimeter.…”