Acute kidney injury (AKI) is the sudden loss of kidney function that results in damage to the proximal and distal convoluted tubular cells over a short period of time (hours to days). AKI is a common health problem that arises in patients during and after severe COVID-19 infection. Although the exact numbers are still being debated, there is clinical evidence that AKI (or subclinical AKI) is a strong predictor of people who, if infected with SARS-CoV-2, may end up requiring renal replacement therapy to slow the progression towards organ failure, a treatment option that is unavailable in many health care settings around the world. A recent review of hospitalized US veterans found that nearly half of people with COVID-19 and AKI had unresolved AKI when the hospital discharged them. Thus, there is an increasing need for an efficient point-of-care detection method which allows individuals to detect early development of AKI and monitor kidney health for extended periods after recovery from COVID-19 infection.  Here we report two prototype urinary tests which can be used to monitor changes in urinary N-acetyl-β-D-glucosaminidase (NAG), a urinary enzyme biomarker of early-stage AKI. The first approach describes a colorimetric assay which contains a NAG substrate that produces a colored dye which can be captured by anion exchange filter paper for naked eye detection and cell phone transmission of the test result. The second test uses Surface Enhanced Raman Spectroscopy (SERS) to detect a SERS-active molecule that is captured by nanoparticles after NAG catalyzed substrate cleavage. Enzyme kinetic data and limit of detection measurements show that both tests have promise as new point-of-care detection methods to monitor changes in urinary NAG levels as a measure of kidney health and early-stage AKI.

Protype colorimetric and SERS methods for detection of urinary enzyme biomarker of acute kidney injury

ACS Fall 2021

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