Diagnosing urinary tract infection (UTI) conventionally requires precise specimen collection, handling of infectious human waste, controlled urine storage, and timely transportation to modern laboratory equipment for analysis. Here we investigate holographic lens-free imaging as a potential solution for analyzing unmodified urine at the patient bedside.
We implemented a simple lens-free holographic imaging system utilizing a 405-nm laser diode, a 2-mm thick sample chamber, and a consumer-grade CMOS image sensor. Using this system, we compared images reconstructed from holograms to conventional microsopy images. We also assessed the accuracy and dynamic range of estimating volumetric urine particulate concentrations from holograms.
We found that this approach is highly sensitive to red and white blood cell concentrations, linearly correlating to ground truth hemacytometer measurements over 3 orders of magnitude. We showed that E. coli concentrations could be determined by counting bacteria from 103 to 105 cells/mL, and up to 108 cells/mL by analyzing hologram texture. Measurements of blood cell concentrations were relatively insensitive to changes in bacteria concentrations of over seven orders of magnitude. Lastly, we found clear differences between UTI-positive and UTI-negative urine from human patients.
These results show promise for holographic imaging as a tool for urine screening, establishing the feasibility of a solution for early, point-of-care detection of UTI and other pathological processes.