Prostate Specific Antigen Biosensor Based on Long Range Surface Plasmon-Enhanced Fluorescence Spectroscopy and Dextran Hydrogel Binding Matrix

Abstract

A new biosensor based on surface plasmon-enhanced fluorescence spectroscopy (SPFS), which employs long-range surface plasmons (LRSP) and a photo-cross-linkable carboxymethyl dextran (PCDM) hydrogel binding matrix, is reported. LRSPs are surface plasmon modes that propagate along a thin metallic film with orders of magnitude lower damping compared to regular surface plasmons. Therefore, their excitation provides strong enhancement of the intensity of the electromagnetic field and a greatly increased fluorescence signal measured upon binding of fluorophore-labeled molecules on the sensor surface. In addition, these modes exhibit highly extended evanescent fields penetrating up to micrometers in distance from the metallic sensor surface. Therefore, a PCDM hydrogel with approximately micrometer thickness was anchored on the sensor surface to serve as the binding matrix. We show that this approach provides large binding capacity and allows for the ultrasensitive detection. In a model experiment, the developed biosensor platform was applied for the detection of free prostate specific antigen (f-PSA) in buffer and human serum by using a sandwich immunoassay. The limit of detection at the low femtomolar range was achieved, which is approximately 4 orders of magnitude lower than that for direct detection of f-PSA based on the monitoring of binding-induced refractive index changes.

Surface plasmon-enhanced fluorescence on Au nanohole array for prostate-specific antigen detection

“…As illustrated in Figure 1A, LSP and PSP on the gold surface were excited by attenuated total reflectance, 37 where the transverse magnetic (p-polarized) beam emitted from a HeNe laser (λ=632.8 nm) was coupled into the attenuated total reflectance through an LASFN9 glass prism (Schott Glass Inc., Mainz, Germany). At the contact area to the prism base, the sensing substrate was applied with matching oil (n=1.700; Cargille Labs, Cedar Grove, NJ, USA) to match its reflective index with the prism.…”

“…The sensitivity of this method is comparable with that of the long-range SP-enhanced fluorescence based on threedimensional hydrogel-binding matrix (34 fM). 37 However, it is two orders higher sensitivity than SP resonance direct detection (LOD of 30 pM). 50 Overall, the coexcitation of LSP and PSP could significantly improve the field intensity around the nanostructures and thus improve fluorescence enhancement as compared with the case where only LSP was excited.…”

“…The field enhancement by PSP could be further improved up to 60-fold by the excitation of long-range SP on a gold thin film coated on a dielectric layer having its refractive index close to water. [34][35][36][37] Compared with the PSP on a metallic thin film, the LSP on metallic nanostructures typically offers higher confinement of the field with a penetration depth L p from several to tens of nanometers, which is about tenfold lower than the conventional PSP (L p =180 nm). Such a highly confined LSP field on nanostructures has demonstrated a fluorescence enhancement of about 10-to 200-fold on an averaged area and 1,300-fold for a single dye positioned on the hot spot of a bowtie nanoantenna.…”

Influence of Plasma Polymerized Dielectric Buffer Layer and Gold Film on the Excitation of Long-Range Surface Plasmon Resonance

“…Due to their stronger surface electromagnetic field enhancement and longer penetration depth from metallic surface, long-range surface plasmon resonance (LRSPR) sensors are believed to be particularly beneficial for the real-time monitoring of cellular behaviors [1][2][3][4], as well as the excitation of fluorescence/Raman dyes in a 3D matrix [5][6][7][8]. Thus, a great deal of effort has been placed on the fabrication and application of LRSPR sensors during the past two decades [9][10][11].…”

Sensitive Electrochemical Prostate Specific Antigen Aptasensor: Effect of Carboxylic Acid Functionalized Carbon Nanotube and Glutaraldehyde Linker

“…Prostate canceri st he second leading cause of cancer mortality amongt he male population that consists of fourteen percent of all cancers and sixth percento ft he total cancer deathsi nm ales [1].P rostates pecific antigen (PSA) has shown to be the mostv alidated serum marker for the early detection of prostate and breast cancers and monitor for disease recurrence after treatment [2,3].I ti s a3 3-kDas ingle chain glycoprotein that exists naturallyi n the human serum, either free or in complex with various proteinase inhibitors.B lood total PSA concentrations above av alue of 4ng/ml is often suspected to the appearance of tumors in the prostate [4].T he early detection of PSA at organ-confined stage leads to the early diagnosis and management of prostate cancer, and so,i ncreasese xpectancy of complete patientr ecovery [5].T herefore,t he development of reliable diagnostic tests for the rapid determinationo fP SA has recentlya ttracted substantial research efforts of the scientific community [6].Avariety of techniques have been used for the determinationo f PSA, including fluorescence methods [ 7],i mmunochromatography test [8],s urface plasmon resonance [9],s urface-enhanced ramans cattering (SERS) [10],s urface plasmon fluorescence spectroscopy [11],c hemiluminescence [12],f ield effect transistors [13],m icro-cantilevers [14] and electrochemical techniques [4,[15][16][17][18].R ecently, electrochemical methodsh ave received great attention due to their inherent advantages of simplicity,e ase of miniaturization, rapid response,h igh sensitivity, and relatively low cost [19][20][21].E lectrochemical aptasensors are an ew kind of electrochemical sensors that use aptamers as recognition elements.A sit is well known, aptamers refer to single-stranded DNAo rR NA oligonucleotides that can selectively bind to ab road range of targets,i ncluding metal ions,s mall molecules,p eptides, proteins, and even complex targets such as whole cells and materials surfaces [22,23].A ptamers are selected using systematic evolution of ligands by exponential enrichment (SELEX) [24,25].O wing to numerous advantagess uch as high stability (especially DNAa ptamers), small size, ease of modificat...…”