JUN 16, 2020
This study evaluated a smartphone-based, gold nanoparticle-based immunoassay paper sensor for identifying a biomarker for diabetic retinopathy (DR).
The assay is designed to quantify urine 8-hydroxy-2'-deoxyguanosine (8-OHdG), a byproduct of in vivo oxidative DNA damage. Color changes on this nanoparticle-based paper strip are discernible on a smartphone camera photograph. Researchers collected urine specimens from 97 patients who were also getting DR screening exams and fundus photos. The aim was to assess the potential utility of urinary 8-OHdG as a useful marker and to test the paper strip immunoassay as a screening tool for DR.
The immunoassay nanoparticle-based paper strips were found to be accurate, precise and stable in measuring 8-OHdG. The average concentration of 8-OHdG was 2.5 times greater in the high-risk group than in the low-risk group (55 vs. 22 ng/mg of creatinine). Using screening cutoff values for creatinine (>50 ng/mg) and urine creatinine (>1.5 mg) minimized screen failures, with 91% sensitivity and 81% specificity.
The 8-OHdG biomarker target for this assay did not show a linear correlation between concentration and increasing DR severity; other biomarkers such as Ang-2, however, may more strongly correlate. The authors are assessing other potential biomarkers and postulate that the presence of 2 or more biomarkers may be the most effective DR screening. However, as proof of concept, this paper lateral flow immunoassay offers a cheap at-home method of testing that was accurate and precise.
Treatment for DR is best when instituted early, but many diabetics do not undergo regular DR screening. This shelf-stable paper immunoassay would allow for at-home testing with simple smartphone assessment. This could help enhance screening efforts since annual ophthalmic examinations for diabetics can be difficult in terms of compliance. With further refinement—possibly by incorporating additional biomarkers—this assay could be a way to improve DR screening in the future. Larger trials are needed to identify appropriate cutoff values and assess sensitivity and specificity.