## 2 Materials and Methods  
A 57-year-old woman was attending our unit at the University of Messina, Italy, on January 2021 because her husband's observation of seemingly blue discoloration of the urine catheter and urine bag which occurred every time a few days after the silicon catheter change, apart from the first three changes. The medical history of our patient is very complicated because she was suffering from various pathologies. See in the Supplementary Materials for the comprehensive medical history and clinical data of the patient. Urine specimens from both the patient's renal pelvis and urine bag were collected in sterile containers in the morning and analyzed at room temperature within 1 h of collection to avoid changes, such as an increase in pH (due to breakdown of urea to ammonia), a decrease in bilirubin (due to light exposure), and changes in color (due to oxidation or reduction reactions). Urine specimens were neither treated nor processed. All urine specimens were analyzed by using RS. Sterile urine bags were used to collect the patient's urine. The bags, with a capacity of 2000 mL, and the tubes are made of polyvinyl chloride (PVC). PVC is a synthetic thermoplastic material, chemically nonreactive, obtained by polymerization of vinyl chloride monomers. Sterility inside the bags is maintained by the presence of a nonreturn valve that prevents urine back flow into the indwelling urinary catheter. Five \"blue\" discolored bags and one sterile urine bag, as a control, were cut into 1 cm\({}^{2}\) square samples, using a sterile scissor. All samples were analyzed by using SEM + EDX. Raman measurements were performed by using a DXR-SmartRaman Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). The experimental setup was equipped with 180-degree sampling accessory. The spectra were acquired using a diode laser source with the excitation wavelength of 780 nm. All Raman spectra were acquired over the wavenumber range of 3300-200 cm\({}^{-1}\) with an estimated resolution between 4.7 and 8.8 cm\({}^{-1}\), and irradiated with a laser power of 24 mW, coming out from a 50-\(\upmu\)m spot (estimated spot size 3.1 \(\upmu\)m). The estimated data spacing was 1.9285 cm\({}^{-1}\). To obtain high signal-to-noise ratio (S/R) spectra, the Raman spectrum of each sample was obtained in triplicate after collecting 32 sample exposures for each spectrum, and the duration of each exposure during data collection was set equal to 60.0 s. Total acquisition time was 32 min for each spectrum. All Raman spectra were corrected for fluorescence by subtracting a fifth-order polynomial via a least squares fit, and also for cosmic ray artifacts. All Raman spectra were stored in.spa format, and the post-processing analyses were performed by using the Omnic For Dispersive Raman version 9.1.24 software (Thermo Fisher Scientific Madison, WI, USA). When the acquisition of the Raman spectra was complete, the average spectrum for each sample was calculated, and a baseline subtraction was applied (polynomial spline) to a manually chosen point in the wavenumber range 300-2000 cm\({}^{-1}\). Each 1-cm\({}^{2}\) square bag sample was mounted on an adhesive black carbon tab, pre-mounted on the sample holder, and then analyzed by an FEI Quanta 450 FEG Thermofisher Scientific Scanning Electron Microscope to evaluate its morphological characteristics. This is a field emission gun--scanning electron microscope (FEG-SEM) used for high-resolution imaging (morphological and compositional) of both conductive and non-conductive specimens at the nanometer-scale resolution and for semi-quantitative X-ray microanalysis. We used it in the \"low vacuum mode\" (LV), where electrically non-conductive samples can be imaged without the need of a conductive layer (e.g., carbon, gold etc.). Each sample surface was scanned in the X-Y direction using the electron beam generated by the electron gun. The SEM measurements were conducted at 25.5 kV.