SERS-based quantification of albuminuria in the normal-to-mildly increased range

Abstract

We developed a SERS-based method for the screening of albuminuria in the sub-microalbuminuria interval. We show the potential of SERS for absolute quantification of albumin.

Breast Cancer Diagnosis by Surface-Enhanced Raman Scattering (SERS) of Urine

“…Conversely, the chemisorption of proteins can also be favoured in the detriment of purine metabolites by modifying the nanoparticles with iodide, as shown recently in our study regarding albumin detection in urine [22]. It is worth mentioning that this strategy works well only for biofluids containing low concentrations of proteins such as urine [22].…”

“…No aggregation of the hya-AgNPs was observed by the addition of Ca 2+ up to 10 −4 M. To test the stability of the hya-AgNPs after their supplementary activation with Ca 2+ up to 10 −4 M, we acquired UV-Vis absorption spectra of nanoparticles before and after activation with Ca 2+ 10 −4 M. The UV-Vis spectrum of hya-AgNPs showed the characteristic plasmonic resonance band at 408 nm ( Figure 2), which did not suffer any significant shift after the SERS-activation of the colloid. Adding cations such as Ca 2+ or Mg 2+ to the silver colloid promotes the chemisorption of anionic species (including purine metabolites) to the silver surface and the switching on of the SERS effect, without necessarily aggregating the nanoparticles, as shown recently by us [19,22]. For instance, adding Ca 2+ 10 −4 M leads to intense SERS spectra of uric acid 10 −4 M, while in the absence of Ca 2+ , the spectra are much weaker ( Figure S1).…”

“…The average SERS spectra of urine samples from breast cancer patients and controls along with the difference spectrum are presented in Figure 3. The standard deviation of the difference spectrum, which is a measure of the robustness of the separation between the groups, is presented as a grey shaded area Adding cations such as Ca 2+ or Mg 2+ to the silver colloid promotes the chemisorption of anionic species (including purine metabolites) to the silver surface and the switching on of the SERS effect, without necessarily aggregating the nanoparticles, as shown recently by us [19,22]. For instance, adding Ca 2+ 10 −4 M leads to intense SERS spectra of uric acid 10 −4 M, while in the absence of Ca 2+ , the spectra are much weaker ( Figure S1 in the Supplementary Materials).…”

“…The SERS signature of the urine samples suggests that the main class of metabolites to chemisorb onto the metal surface is represented by purine metabolites [18,24]. We have recently showed that cations such as Ca 2+ or Mg 2+ facilitate the specific adsorption of anionic species, including citrate and chloride ions, which chemisorb onto the nanoparticles in the order of their relative affinity for the activated metal surface [19,22]. Moreover, the SERS activating effect does not depend on the aggregation of the nanoparticles, as evidenced by the absence of a measurable shift in the plasmon resonance after the addition of Ca 2+ 10 −4 M (Figure 2).…”

“…In contrast to the study by del Mistro et al [11], which filtered the urine using centrifugal filter devices for eliminating proteins, our strategy allowed the acquisition of intense SERS spectra of purine metabolites without any filtering step, since the Ca 2+ added to the solution facilitated the specific adsorption of purine metabolites to the detriment of proteins traces [19,22]. Conversely, the chemisorption of proteins can also be favoured in the detriment of purine metabolites by modifying the nanoparticles with iodide, as shown recently in our study regarding albumin detection in urine [22]. It is worth mentioning that this strategy works well only for biofluids containing low concentrations of proteins such as urine [22].…”