Cancer Marker Immunosensing through Surface-Enhanced Photoluminescence on Nanostructured Silver Substrates

Abstract

Nanostructured noble metal surfaces enhance the photoluminescence emitted by fluorescent molecules, permitting the development of highly sensitive fluorescence immunoassays. To this end, surfaces with silicon nanowires decorated with silver nanoparticles in the form of dendrites or aggregates were evaluated as substrates for the immunochemical detection of two ovarian cancer indicators, carbohydrate antigen 125 (CA125) and human epididymis protein 4 (HE4). The substrates were prepared by metal-enhanced chemical etching of silicon wafers to create, in one step, silicon nanowires and silver nanoparticles on top of them. For both analytes, non-competitive immunoassays were developed using pairs of highly specific monoclonal antibodies, one for analyte capture on the substrate and the other for detection. In order to facilitate the identification of the immunocomplexes through a reaction with streptavidin labeled with Rhodamine Red-X, the detection antibodies were biotinylated. An in-house-developed optical set-up was used for photoluminescence signal measurements after assay completion. The detection limits achieved were 2.5 U/mL and 3.12 pM for CA125 and HE4, respectively, with linear dynamic ranges extending up to 500 U/mL for CA125 and up to 500 pM for HE4, covering the concentration ranges of both healthy and ovarian cancer patients. Thus, the proposed method could be implemented for the early diagnosis and/or prognosis and monitoring of ovarian cancer.

Superoxide Dismutase Detection on Silver Nanostructured Substrates through Surface-Enhanced Spectroscopic Techniques

“…The substrates utilized in this work were fabricated with the MACE method, and included SiNWs decorated with either Ag dendrites or Ag nanoparticle aggregates. The substrates with the Ag dendrites were selected for the SEF measurements while those with the Ag aggregates were employed for the SERS measurements, based on previous findings that indicated Ag dendrites were more effective in SEF, whereas aggregates exhibited a higher signal and an enhanced reproducibility in SERS measurements [40,41].…”

“…For this reason, two distinct configurations of silver nanoparticles were fabricated on silicon surfaces with a simple metal-assisted chemical etching process and evaluated as substrates for the detection of SOD. Our team has already successfully employed these substrates for the determination of two oxidative stress markers, namely glutathione and malondialdehyde, and for the ovarian cancer markers Ca125 and HE4, indicating the potential of these metallic nanostructures in the detection of biological molecules at low concentrations [40,41]. The protocol for SOD determination was based on a competitive immunoassay configuration, and two different signal enhancement approaches were investigated.…”