SERS for Detection of Proteinuria: A Comparison of Gold, Silver, Al Tape, and Silicon Substrates for Identification of Elevated Protein Concentration in Urine

Abstract

Excessive protein excretion in human urine is an early and sensitive marker of diabetic nephropathy and primary and secondary renal disease. Kidney problems, particularly chronic kidney disease, remain among the few growing causes of mortality in the world. Therefore, it is important to develop an efficient, expressive, and low-cost method for protein determination. Surface enhanced Raman spectroscopy (SERS) methods are potential candidates to achieve these criteria. In this paper, a SERS method was developed to distinguish patients with proteinuria from the healthy group. Commercial gold nanoparticles (AuNPs) with diameters of 60 nm and 100 nm, and silver nanoparticles (AgNPs) with a diameter of 100 nm were tested on the surface of four different substrates including silver and gold films, silicon, and aluminum tape. SERS spectra were acquired from 111 unique human urine samples prepared and measured for each of the seven different nanoparticle plus substrate combinations. Data analysis by the PCA-LDA algorithm and the ROC curves gave results for the diagnostic figures of merits. The best sensitivity, specificity, accuracy, and AUC were 0.91, 0.84, 0.88, and 0.94 for the set with 100 nm Au NPs on the silver substrate, respectively. Among the three metal substrates, the substrate with AuNPs and Al tape performed slightly worse than the other three substrates, and 100 nm gold nanoparticles on average produced better results than 60 nm gold nanoparticles. The 60 nm diameter AuNPs and silicon, which is about one order of magnitude more cost-effective than AuNPs and gold film, showed a relative performance close to the performance of 60 nm AuNPs and Au film (average AUC 0.88 (Si) vs. 0.89 (Au)). This is likely the first reported application of unmodified silicon in SERS substrates applied for direct detection of proteins in any biofluid, particularly in urine. These results position silicon and AuNPs@Si in particular as a perspective SERS substrate for direct urine analysis, including clinical diagnostics of proteinuria.

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“…90,93 Furthermore, labelfree SERS exhibits high sensitivity and selectivity when combined with a labeled antibody-antigen system. [94][95][96] As shown in Fig. 3(iii), taking Au NPs on a bowl-like ZrO 2 substrate as an example, target analytes can SERS-active reporters, and the hotspots in each nanobowl enhance the SERS signal.…”

Power of Light: Raman Spectroscopy and Machine Learning for the Detection of Lung Cancer

“…Aluminum foil offers high reflectivity that increases the Raman signal by the excitation laser light reflected from the sample; 11 stability that makes it a good choice for holding and stabilizing samples during analysis; flexibility regarding easy shaping or molding to fit the sample holder; a low background signal that helps minimize interference from unwanted signals during analysis; 12 and cost-effectiveness that makes it a practical option for routine Raman analysis.…”

Immunoassays: Analytical and Clinical Performance, Challenges, and Perspectives of SERS Detection in Comparison with Fluorescent Spectroscopic Detection

“…There can be direct and indirect SERS detection configurations [17]. Direct SERS does not apply a sensing molecule that would bind to the analyte molecule (e.g., antibody, aptamer) and the analyte is bound/absorbed to the substrate directly [18,19]. In comparison to direct SERS, indirect SERS, including immunoassays with SERS detection, typically allows a better limit of detection (LOD), at least in bioanalytical applications, because there is better binding of the analyte to the substrate with the help of a capture antibody or aptamer.…”

“…CDs' desirable biocompatibility allows for their application in in vivo and in vitro cell imaging, as well as in the detection of cancer biomarkers [151]. Sultangaziyev et al noted the significant fluorescence enhancement in single E. coli bacteria cells labeled with composite CdSeS/ZnS, with a general tendency towards the enhancement factor being reversely proportional to cyto-toxicity [18,152]. The measurements of the contrast ratios at both 532 and 633 nm excitation were used (1.0-1.2) to explain the unsatisfactory performance of MEF in labeling bacteria cells, due to the toxicity of CdTe QDs [152].…”

“…The solution to this problem may be found by using alternative substrates such as aluminum or silica. Bukasov's group performed research, according to which substrates coated with these compounds can also provide highly sensitive results in the detection of proteins in biological fluid, especially in urea [18]. To obtain time-dependent information about analytes using SERS-based IA detection, it is necessary to carry out a number of repeated measurements at different time intervals.…”