Optical spectroscopy based urine analysis for disease diagnosis

Abstract

Urine is a clinically important and easily accessible body-fluid having extensive diagnostic information about the health status of an individual. Human urine specimen has been subjected to analysis for different disease diagnosis since ancient times. In general, urine consists of more than 95% water, several non-protein nitrogenous compounds (NPNs) such as urea, creatinine, uric acid etc., trace amounts of proteins, hormones, enzymes, bacteria, metabolites, and some inorganic ions such as chloride, sodium, potassium etc. The varying concentration of different constituents or metabolites present in urine identify a wide range of disorders in their early stages such as kidney disorders, urinary tract infections (UTI), liver diseases, diabetes, cancers etc. In current medical practice, different analytical methods such as high-performance liquid chromatography, liquid chromatography-mass spectrometry/mass spectroscopy, gas chromatography, capillary zone electrophoresis etc. have been widely used to estimate the concentration changes of metabolites present in urine. However, all these methods follow sequences of sample preparation steps, need multiple reagents, and specialized training. Further, these methods require sophisticated, bulky and expensive instruments for urine analysis. Therefore, there is a need for an alternate approach which is rapid, reliable, inexpensive, and does not require any special sample preparation. Recently, optical techniques such as Raman and fluorescence spectroscopy have shown immense potential for rapid urine analysis or urinalysis by overcoming the aforementioned limitations. These techniques are able to correlate specific biochemical changes of the analytes present in urine with their normal and disease conditions. The simple instrumentation, cost-effectiveness, and molecular sensitivity of these techniques make them as suitable analytical tools for human health monitoring. Despite the promising development, the clinical applications of optical techniques are limited due to the poor signal collection and lack of reproducibility in the measured signal intensities from the analytes present in body fluids including urine. These limitations could be addressed by incorporating the nanotechnology and improved optical signal detection strategies. The goal of the present thesis is to investigate the use of optical spectroscopy in urine analysis for rapid and reliable disease diagnosis. In this regard, an attempt has been made for the quantitative determination of trace amounts of analytes present in urine using drop-coating deposition Raman spectroscopy (DCDRS) and nano-trap enhanced Raman spectroscopy (NTERS). DCDRS is a comparatively new variant of Raman spectroscopy in which analytes or molecules get deposited in ring shape pattern on an appropriate substrate due to the coffee ring effect and improves the sensitivity of Raman signal measurement from analytes. NTERS is a new Raman signal enhancement technique in which nanoclusters of metallic nanoparticles are formed at the focus of the excitation laser beam due to optical trapping. The analytes get trapped within these nanoclusters at the peripheral region (laser beam focus) of the dried drop of solution where maximum deposition of the solute has been occurred. The Raman signals measured from these analytes trapped within the nanoclusters get highly enhanced due to the both surface plasmon and coffee ring effects. In the subsequence of these studies the fluorescence photobleaching dynamics of urine samples has been studied and used for the oral cancer diagnosis.