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Immunosensing of cancer markers through surface-enhanced photoluminescence on nanostructured silver substrates
1, 2 , 1 , 3 , 3 , 4 , 3 , 4 , 2 , 1 , * 1 , 5 , 5
1  Immunoassays/Immunosensors Lab, Institute of Nuclear & Radiological Sciences & Technology, Energy & Safety, NCSR “Demokritos”, 15341 Aghia Paraskevi, Greece
2  Department of Chemistry, National and Kapodistrian University of Athens, Zografou 15771, Greece
3  Section of Condensed Matter Physics, Department of Physics, National and Kapodistrian University of Athens, University Campus, 15784 Athens, Greece
4  Institute of Nanoscience and Nanotechnology, NCRS “Demokritos”, 15341 Aghia Paraskevi, Greece
5  Molecular Diagnosis Department, INVITROLABS S.A., Peristeri 12251, Greece
Academic Editor: Evgeny Katz (registering DOI)

Nanostructured surfaces of noble metals enhance considerably the intensity of photoluminescence from molecules immobilized on them providing a mean for their sensitive detection. The combination of such surfaces with immunochemical techniques provides assays that are characterized by high sensitivity and specificity. Thus, the aim of this work was to fabricate and evaluate nanostructured silver surfaces as substrates for the immunochemical detection of two ovarian cancer markers, carbohydrate antigen 125 (Ca125) and human epididymis protein 4 (HE4). The substrates were prepared following a metal-assisted chemical etching procedure on silicon wafers resulting in the creation of silicon nanowires decorated with either silver dendrites or silver nanoparticles. Non-competitive immunoassays for detection of the biomarkers were developed on these substrates using pairs of highly specific mouse monoclonal antibodies; one as capture and the other as detection. The detection antibodies were biotinylated to allow detection of immunocomplexes through reaction with streptavidin labeled with fluorescent labels for photoluminescence measurements. The measurements were performed employing an in-house developed low-cost optical set-up. It was found that, the higher signals were received using substrates with silver dendrites rather than with silver nanoparticles. The detection limits achieved for Ca125 and HE4 were 10 U/mL and 0.3 ng/mL, respectively, and the linear dynamic ranges extended up to 200 U/mL for Ca125 and 2.5 ng/mL for HE4, covering the required clinical concentration ranges. The nanostructured silver surfaces are currently evaluated as substrates for the development of multi-analyte assays targeting both ovarian cancer markers.

Keywords: nanostructured silver substrates; photoluminescence; immunoassay; Ca125; human epididymis protein 4