Molybdenum blue mediated photothermal immunoassay for CEA detection based on Ag4P2O7@Ag nanocomposites

A photothermal immunoassay was built for tumor marker detection based on Ag₄P₂O₇@Ag nanocomposites. Ag₄P₂O₇@Ag nanomaterials were synthesized by precipitation-photoreduction reaction, and characterized by transmission electron microscope (TEM), scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray photoelectron spectra (XPS) and X-ray powder diffraction (XRD). Come about PO₄^3- derived from Ag₄P₂O₇@Ag under acidic conditions react with ammonium molybdate in the action of reductant generating molybdenum blue. The photothermal change is due to molybdenum blue solution depending on the concentration of carcinoembryonic antigen (CEA) in immunoassay. Under optimal conditions, there is a linear relation between ΔT and CEA concentration in the range of 1 pg mL^-1-40 ng mL^-1 with the detection limit of 0.33 pg mL^-1. Meanwhile, the developed photothermal immunoassay displays preferable selectivity, repeatability, and stability.

Metal Nanoparticle and Quantum Dot Tags for Signal Amplification in Electrochemical Immunosensors for Biomarker Detection

With the increasing importance of healthcare and clinical diagnosis, as well as the growing demand for highly sensitive analytical instruments, immunosensors have received considerable attention. In this review, electrochemical immunosensor signal amplification strategies using metal nanoparticles (MNPs) and quantum dots (Qdots) as tags are overviewed, focusing on recent developments in the ultrasensitive detection of biomarkers. MNPs and Qdots can be used separately or in combination with other nanostructures, while performing the function of nanocarriers, electroactive labels, or catalysts. Thus, different functions of MNPs and Qdots as well as recent advances in electrochemical signal amplification are discussed. Additionally, the methods most often used for antibody immobilization on nanoparticles, immunoassay formats, and electrochemical methods for indirect biomarker detection are overviewed.

Introducing graphitic carbon nitride nanosheets as supersandwich-type assembly on porous electrode for ultrasensitive electrochemiluminescence immunosensing

Biomarkers in blood or tissue provide essential information for clinical screening and early disease diagnosis. However, increasing the sensitivity of detecting biomarkers remains a major challenge in a wide variety of electrochemical immunoassays. Herein, we present an electrochemiluminescence (ECL) immunosensing strategy with 1: Nⁿ amplification ratio (target-to-signal probe) for biomarkers detection on a porous gold electrode. The high porosity of the electrode surface provides enough bonding sites for capturing the target biomolecules and thus many DNA labels can be introduced. On the basis of this concept, a great number of graphitic carbon nitride (g-C₃N₄) nanosheets are employed to create a supersandwich-type assembly on a porous electrode via the DNA hybridization process. Furthermore, compared with the traditional sandwich immunoassay (the ratio of target-to-signal probe is 1 : 1), the supersandwich construction can introduce a large number of signal probes, thus resulting in a highly improved sensitivity. The proposed ECL immunosensor exhibits an excellent performance in a concentration range from 0.01 fg mL^-1 to 1 μg mL^-1 with an ultralow detection limit of 0.001 fg mL^-1 (S/N = 3) and excellent selectivity. This sensing strategy could be developed into a real-time assay for the disease-related molecular targets, with many practical applications in biotechnology and life science.

In Situ Growing Triethanolamine-Functionalized Metal-Organic Frameworks on Two-Dimensional Carbon Nanosheets for Electrochemiluminescent Immunoassay

A facile strategy for in situ growing triethanolamine (TEOA)-functionalized metal-organic framework (TEOA@MOF) on the two-dimensional graphene oxide (GO) or g-C₃N₄ nanosheets via the self-assembly technique was introduced. In this method, Zn²⁺ was first attached on the carbon nanosheets by electrostatic interaction; then, trimesic acid (H₃btc) acted as the complex agent and TEOA as a base for the deprotonation of H₃btc and a template, which leads to in situ growing the MOF on the carbon nanosheets obtaining a sandwich-like structure. Different types of surface analysis techniques were employed to characterize the GO-TEOA@MOFs and g-C₃N₄-TEOA@MOFs nanomaterials fabricated. The GO-TEOA@MOFs or g-C₃N₄-TEOA@MOFs nanomaterial-modified electrode brings out obviously enhanced electrochemiluminescence (ECL) behaviors due to numerous TEOA in the framework structures. Specifically, both TEOA and GO can serve as the co-reactants for the ECL system of Ru(bpy)₃²⁺ and have the synergic effect of enhancing the signal. Based on the GO-TEOA@MOFs modified electrodes, we developed a sensitive and rapid label-free ECL immunoassay strategy for human copeptin, and the linear range was 5 pg mL^-1 to 500 ng mL^-1 as well as the limit of detection was 360 fg mL^-1. This work exhibits excellent specificity and good stability of the prepared immunosensor in the practical sample determination, demonstrating it can serve as a very promising method for the clinical diagnostics of acute myocardial infarction disease.

A microfluidic colorimetric immunoassay for sensitive detection of altenariol monomethyl ether by UV spectroscopy and smart phone imaging

A novel microfluidic colorimetric immunoassay was developed using gold nanoparticles (GNPs) for indicating different concentrations of altenariol monomethyl ether (AME), and UV spectroscopy and smart phone imaging for monitoring color change of the GNPs. Norland Optical Adhesive 81 (NOA 81) was used for simple and rapid fabrication of the microfluidic chip. AME-BSA modified magnetic nanoparticles (MNPs-BSA-AME) were used as capture probe and the self-magnetism for rapid separation and purification. AME monoclonal antibodies modified gold nanoparticles (GNP-mAbs) which dried on conjugate pad were used as detection probe and the self-catalyst for signal amplification. Under the optimal conditions, the proposed microfluidic colorimetric immunoassay was able to detect AME as low as 12.5 pg/mL for UV spectroscopy (574 nm), and 200 pg/mL for smart phone imaging. The total analysis time is less than 15 min. The immunoassay also has a lower cross-reactivity to AME analogues. It was also evaluated by analyzing fruit samples spiked with AME. The recoveries ranged from 91.19% to 94.15% for UV spectroscopy, and from 90.63% to 93.9% for smart phone imaging. This method can be used for rapid, sensitive, low-cost and portable point-of care testing (POCT) of other mycotoxins or haptens in food samples.

Dispersing gold nanoparticles on thiolated polyaniline-multiwalled carbon nanotubes for development of an indole-3-acetic acid amperometric immunosensor

An amperometric immunosensor based on new thiolated bionanocomposite with a high dispersion of gold nanoparticles (AuNPs) for the sensitive detection of indole-3-acetic acid (IAA) is being reported herein. Briefly, a thiolated nanocomposite was prepared via the microwave-assisted thiol-ene reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) with oxidized polyaniline (PANI), which was synthesized in the presence of multiwalled carbon nanotubes (MWCNTs), yielding thiolated polyaniline (TPANI)-MWCNTs. Further, AuNPs were deposited on the TPANI-MWCNTs by microwave-assisted method to obtain a AuNPs/TPANI-MWCNTs nanocomposite. Finally, the thiolated bionanocomposite film was constructed via the specific chemical reaction between boronic acid functionalized AuNPs and the vicinal diol functionalized AuNP labeled immunoglobulin G (IgG-AuNPs). The change in the reduction peak current of Fe(CN)₆ ^3- was used to monitor the immunoreaction between IAA and antibody. The TPANI-MWCNT nanocomposites uniformly disperse AuNPs, IgG-AuNPs and anti-IAA-AuNPs, leading to the amplification of the signal of the immunosensor. Fourier transform infrared spectra (FTIR), cyclic voltammetry (CV), transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and differential pulse voltammetry (DPV) were used to characterize the nanocomposite film and the stepwise modification of the immunosensor. The prepared thiolated bionanocomposite material has good biocompatibility, a highly uniform dispersion of the AuNPs with a narrow size distribution as verified by TEM, and high load/activity of the immobilized antibody proved via DPV. The fabricated IAA amperometric immunosensor not only exhibits a good linear arrange from 1.0 pg mL^-1 to 10 ng mL^-1 with the limit of detection of 0.97 pg mL^-1 (S/N = 3), but also possesses good selectivity, reproducibility and stability for the detection of IAA.

Photothermal Soft Nanoballs Developed by Loading Plasmonic Cu2- xSe Nanocrystals into Liposomes for Photothermal Immunoassay of Aflatoxin B1

Photothermal effects (PTEs) have been greatly concerned with the fast development of new photothermal nanomaterials. Herein we propose a photothermal immunoassay (PTIA) by taking mycotoxins (AFB1) as an example based on the PTEs of plasmonic Cu2- xSe nanocrystals (NCs). By loading plasmonic Cu2- xSe NCs into liposomes to form photothermal soft nanoballs (ptSNBs), on which aptamer of AFB1 previously assembled, a sandwich structure of AFB1 could be formed with the aptamer on ptSNBs and capture antibody. The heat released from the ptSNBs under NIR irradiation, owing to the plasmonic photothermal light-to-heat conversion through photon-electron-phonon coupling, makes the temperature of substrate solution increased, and the increased temperature has a linear relationship with the AFB1 content. Owing to the large amounts of plasmonic Cu2- xSe NCs in the ptSNBs, the PTEs get amplified, making AFB1 higher than 1 ng/mL detectable in food even if with a rough homemade immunothermometer. The proposal of PTIA opens a new field of immunoassay including developing photothermal nanostructures, new thermometers, PTIA theory, and so on.

Chemical pre-reduction and electro-reduction guided preparation of a porous graphene bionanocomposite for indole-3-acetic acid detection

A porous graphene (PG) bionanocomposite of PG, gold nanoparticles (AuNPs) and anti-indole-3-acetic acid (anti-IAA) antibody for sensitive and label-free amperometric immunoassay of IAA was reported. A PG film was produced by a pre-reduction/electrochemical reduction process on a glassy carbon electrode (GCE) and then a homogeneous AuNPs layer electrodeposition on the PG film. The anti-IAA antibody was immobilized onto the AuNPs through electrostatic adsorption and covalent conjugation. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), cyclic voltammetry (CV), elecro-chemical impedance spectroscopy (EIS), ultraviolet visible spectroscopy (UV-vis) and differential pulse voltammetry (DPV) were used to characterize the PG film and the stepwise modification of the immunosensor. The electrochemical immunosensor exhibited a wide linear range from 2 × 10-11 to 2 × 10-8 g mL-1 with a detection limit of 0.016 ng mL-1 (S/N = 3) and showed significant linearity R2 = 0.9970. In addition, the proposed immunosensor showed acceptable selectivity and has been applied to the determination of IAA in the extract samples of several plant seeds with acceptable relative derivation (%) ranging from -5.25% to 4.24% between the immunosensor and high performance liquid chromatography. The proposed chemical pre-reduction and electro-reduction guided protocol can be extended to the preparation of many other functionalized PG nanocomposite films for wide applications.

Applications of Gold Nanoparticles in Non-Optical Biosensors

Due to their unique properties, such as good biocompatibility, excellent conductivity, effective catalysis, high density, and high surface-to-volume ratio, gold nanoparticles (AuNPs) are widely used in the field of bioassay. Mainly, AuNPs used in optical biosensors have been described in some reviews. In this review, we highlight recent advances in AuNP-based non-optical bioassays, including piezoelectric biosensor, electrochemical biosensor, and inductively coupled plasma mass spectrometry (ICP-MS) bio-detection. Some representative examples are presented to illustrate the effect of AuNPs in non-optical bioassay and the mechanisms of AuNPs in improving detection performances are described. Finally, the review summarizes the future prospects of AuNPs in non-optical biosensors.

An electrochemical immunobiosensor for ultrasensitive detection of Escherichia coli O157:H7 using CdS quantum dots-encapsulated metal-organic frameworks as signal-amplifying tags

We report here cadmium sulfide quantum dots (CdS QDs)-encapsulated metal-organic frameworks as signal-amplifying tags for ultrasensitive electrochemical detection of Escherichia coli O157:H7 (E. coli O157:H7). CdS QDs were encapsulated in zeolitic imidazolate framework-8 (ZIF-8) to form CdS@ZIF-8 muti-core-shell particles by in situ growth of ZIF-8 in the presence of CdS QDs. To specifically recognize E. coli O157:H7 cells, CdS@ZIF-8 particles were coated with polyethyleneimine to introduce amino groups on their surfaces, followed by surface modification of anti-E. coli O157:H7 antibody. A sandwich-type electrochemical immunobiosensor for the detection of E. coli O157:H7 was fabricated using CdS@ZIF-8 particles as signal tags. Cd(II) ions were released from CdS@ZIF-8 tags by HCl leaching, enabling the detection of E. coli O157:H7 by differential pulse voltammetry. Under the optimized conditions, the linear range of the biosensor is from 10 to 10⁸ colony forming units (CFU) per mL for E. coli O157:H7 detection, with the detection limit of 3 CFU mL^-1 (S/N = 3). The sensitivity of the biosensor for E. coli O157:H7 detection using CdS@ZIF-8 particles as signal tags is 16 times that of a biosensor using CdS QDs as signal tags, because the number of CdS QDs labeled to each bacterial cell increases greatly resulting from a great number of CdS QDs encapsulated in each CdS@ZIF-8 label. This method was successfully used to detect E. coli O157:H7 in milk samples.

In situ enzymatic generation of gold for ultrasensitive amperometric sandwich immunoassay of procalcitonin

Procalcitonin (PCT) is an important indicator for bacterial inflammatory diseases, and its sensitive, accurate and rapid detection has important clinical value. On the basis of sandwich immunoassay, glucose oxidase-catalyzed gold deposition and in-situ microliter-droplet anodic stripping voltammetry (ASV) of the enzyme-generated gold directly on the immunoelectrode, the ultrasensitive electrochemical detection of PCT is achieved. A new method of the chemical dissolution of gold by an appropriately diluted aqua regia and the simultaneous cathodic preconcentration of gold on the immunoelectrode is suggested, which gives the better performance for the ASV analysis of gold than the reported one. Under optimized conditions, the ASV peak current is linear with the common logarithm of PCT concentration from 0.05 fg mL^-1 to 500 ng mL^-1, with a limit of detection (LOD, S/N = 3) as low as 0.04 fg mL^-1. Our method has also been used for detection of PCT in serum samples with satisfactory results.

Redox modulation of polydopamine surface chemistry: a facile strategy to enhance the intrinsic fluorescence of polydopamine nanoparticles for sensitive and selective detection of Fe3

In recent years, polydopamine (PDA) nanoparticles have attracted considerable attention in different research fields because of their many fascinating physicochemical properties. However, as an analogue of naturally occurring melanin, PDA nanoparticles (PDANPs) typically exhibit weak fluorescence properties. Herein, we report a facile one-pot method for synthesizing bright blue luminescent PDANPs through the redox modulation of PDA surface chemistry. The composition and morphology of the resultant NPs were systematically characterized by transmission electron microscopy and several spectroscopy methods, which verified the successful fabrication of PDANPs. More importantly, comparative chemical analysis of dopamine polymerization revealed the significant impacts of synthesis conditions and PDA surface chemistry on the luminescence properties of PDANPs. Remarkably, in addition to their excellent water-solubility, salt-tolerance and high photostability under extreme pH conditions, the as-prepared PDANPs possess the highest quantum yield (5.1%) among all the reported intrinsic fluorescent PDANPs. Moreover, based on the coordination interaction between phenolic hydroxyl groups of PDANPs and ferric ions (Fe3+), the synthesized PDANPs were successfully utilized as a turn-off sensing platform for sensitive and selective detection of Fe3+ without using any additional targeting molecules. Upon increasing the Fe3+ concentration in the range from 0.5 to 20 μM, the fluorescence intensity of PDANPs decreased linearly. The detection limit of Fe3+ was 0.15 μM. Finally, this fluorescent sensor was successfully used to determine Fe3+ in natural water samples, showing good prospects for practical applications and may pave the way for the development of new rational methodologies for further enhancing the intrinsic fluorescence of PDA and fabricating other novel fluorescent organic nanoparticles.

Fabrication of Tris(bipyridine)ruthenium(II)-Functionalized Metal-Organic Framework Thin Films by Electrochemically Assisted Self-Assembly Technique for Electrochemiluminescent Immunoassay

A simple strategy for one-step fabrication of tris(bipyridine)ruthenium(II) (Ru(bpy)₃²⁺)-functionalized metal-organic framework (Ru-MOF) thin films using a self-assembly approach assisted by an electrochemical way was introduced. In this protocol, the electrochemically driven cooperative reaction of Ru(bpy)₃²⁺ as an electrochemiluminescent (ECL) probe and a structure-directing agent, trimesic acid (H₃btc) as a ligand, and Zn(NO₃)₂ as the Zn²⁺ source leads to an one-step and simultaneous synthesis and deposition of the MOF onto the electrode surface. Characterization of the Ru-MOF thin films was performed with scanning electron microscopy, Fourier transform infrared, and X-ray photoelectron spectroscopy. Scanning ion conductance microscopy was specially applied in situ to image the topography and thickness of the Ru-MOF thin films. The Ru-MOF thin films as a sensing platform show excellent ECL behavior because of plenty of Ru(bpy)₃²⁺ molecules encapsulated in the frameworks. On the basis of the Ru-MOF modified electrodes, an ultrasensitive label-free ECL immunosensing method for the human heart-type fatty-acid-binding protein has been developed with a wide linear response range (150 fg mL^-1-150 ng mL^-1) and a very low limit of detection (2.6 fg mL^-1). The prepared immunosensor also displayed excellent stability and good specificity in the test of practical samples.

Exploration of Nanoparticle-Mediated Photothermal Effect of TMB-H2O2 Colorimetric System and Its Application in a Visual Quantitative Photothermal Immunoassay

The exploration of new physical and chemical properties of materials and their innovative application in different fields are of great importance to advance analytical chemistry, material science, and other important fields. Herein, we, for the first time, discovered the photothermal effect of an iron oxide nanoparticles (NPs)-mediated TMB (3,3',5,5'-tetramethylbenzidine)-H2O2 colorimetric system, and applied it toward the development of a new NP-mediated photothermal immunoassay platform for visual quantitative biomolecule detection using a thermometer as the signal reader. Using a sandwich-type proof-of-concept immunoassay, we found that the charge transfer complex of the iron oxide NPs-mediated one-electron oxidation product of TMB (oxidized TMB) exhibited not only color changes, but also a strong near-infrared (NIR) laser-driven photothermal effect. Hence, oxidized TMB was explored as a new sensitive photothermal probe to convert the immunoassay signal into heat through the near-infrared laser-driven photothermal effect, enabling simple photothermal immunoassay using a thermometer. Based on the new iron oxide NPs-mediated TMB-H2O2 photothermal immunoassay platform, prostate-specific antigen (PSA) as a model biomarker can be detected at a concentration as low as 1.0 ng·mL-1 in normal human serum. The discovered photothermal effect of the colorimetric system and the developed new photothermal immunoassay platform open up a new horizon for affordable detection of disease biomarkers and have great potential for other important material and biomedical applications of interest.

Detection of microalgae superoxide dismutase (SOD) using a GNRs-based resonance light scattering system

A novel and label-free, gold nanorods (GNRs)-based resonance light scattering system assay has been developed for the detection of microalgae superoxide dismutase (SOD). The method relies on the fact that interactions between microalgae SOD and GNRs can emit strong fluorescence signals. The prepared GNRs were well dispersed in the solution and intracellular SOD was extracted from Microcystis aeruginosa; the SOD was then absorbed on the surface of the GNRs. The results demonstrated that the intensity of the fluorescence signals increased at 595 nm with an increase in the SOD concentration, the optimum pH value was concluded to be 7.8, the optimum concentration of inorganic salt Na⁺ ions was 0.2 mol L^-1, and the reaction system was stable for 50 min. This method offers the advantages of higher sensitivity and selectivity in microalgae protein detection and exhibits great potential for biological diagnosis.

Aptamer-based fluorescent detection of ochratoxin A by quenching of gold nanoparticles

A simple, rapid, low cost and highly sensitive method for the detection of ochratoxin A (OTA) was developed based on the principle that dispersed AuNPs show a better fluorescence quenching effect than aggregated AuNPs.

Selective staining of CdS on ZnO biolabel for ultrasensitive sandwich-type amperometric immunoassay of human heart-type fatty-acid-binding protein and immunoglobulin G

We report on an ultrasensitive metal-labeled amperometric immunoassay of proteins, which is based on the selective staining of nanocrystalline cadmium sulfide (CdS) on ZnO nanocrystals and in-situ microliter-droplet anodic stripping voltammetry (ASV) detection on the immunoelectrode. Briefly, antibody 1 (Ab₁), bovine serum albumin (BSA), antigen and ZnO-multiwalled carbon nanotubes (MWCNTs) labeled antibody 2 (Ab₂-ZnO-MWCNTs) were successively anchored on a β-cyclodextrin-graphene sheets (CD-GS) nanocomposite modified glassy carbon electrode (GCE), forming a sandwich-type immunoelectrode (Ab₂-ZnO-MWCNTs/antigen/BSA/Ab₁/CD-GS/GCE). CdS was selectively grown on the catalytic ZnO surfaces through chemical reaction of Cd(NO₃)₂ and thioacetamide (ZnO-label/CdS-staining), due to the presence of an activated cadmium hydroxide complex on ZnO surfaces that can decompose thioacetamide. A beforehand cathodic "potential control" in air and then injection of 7μL of 0.1M aqueous HNO₃ on the immunoelectrode allow dissolution of the stained CdS and simultaneous cathodic preconcentration of atomic Cd onto the electrode surface, thus the following in-situ ASV detection can be used for immunoassay with enhanced sensitivity. Under optimized conditions, human immunoglobulin G (IgG) and human heart-type fatty-acid-binding protein (FABP) are analyzed by this method with ultrahigh sensitivity, excellent selectivity and small reagent-consumption, and the limits of detection (LODs, S/N=3) are 0.4fgmL^-1 for IgG and 0.3fgmL^-1 for FABP (equivalent to 73 FABP molecules in the 6μL sample employed).

Sensitive Bioanalysis Based on in-Situ Droplet Anodic Stripping Voltammetric Detection of CdS Quantum Dots Label after Enhanced Cathodic Preconcentration

We report a protocol of CdS-labeled sandwich-type amperometric bioanalysis with high sensitivity, on the basis of simultaneous chemical-dissolution/cathodic-enrichment of the CdS quantum dot biolabel and anodic stripping voltammetry (ASV) detection of Cd directly on the bioelectrode. We added a microliter droplet of 0.1 M aqueous HNO₃ to dissolve CdS on the bioelectrode and simultaneously achieved the potentiostatic cathodic preconcentration of Cd by starting the potentiostatic operation before HNO₃ addition, which can largely increase the ASV signal. Our protocol was used for immunoanalysis and aptamer-based bioanalysis of several proteins, giving limits of detection of 4.5 fg·mL⁻¹ for human immunoglobulin G, 3.0 fg·mL⁻¹ for human carcinoembryonic antigen (CEA), 4.9 fg·mL⁻¹ for human α-fetoprotein (AFP), and 0.9 fM for thrombin, which are better than many reported results. The simultaneous and sensitive analysis of CEA and AFP at two screen-printed carbon electrodes was also conducted by our protocol.

Gold core@silver semishell Janus nanoparticles prepared by interfacial etching

Gold core@silver semishell Janus nanoparticles were prepared by chemical etching of Au@Ag core-shell nanoparticles at the air/water interface. Au@Ag core-shell nanoparticles were synthesized by chemical deposition of a silver shell onto gold seed colloids followed by the self-assembly of 1-dodecanethiol onto the nanoparticle surface. The nanoparticles then formed a monolayer on the water surface of a Langmuir-Blodgett trough, and part of the silver shell was selectively etched away by the mixture of hydrogen peroxide and ammonia in the water subphase, where the etching was limited to the side of the nanoparticles that was in direct contact with water. The resulting Janus nanoparticles exhibited an asymmetrical distribution of silver on the surface of the gold cores, as manifested in transmission electron microscopy, UV-vis absorption, and X-ray photoelectron spectroscopy measurements. Interestingly, the Au@Ag semishell Janus nanoparticles exhibited enhanced electrocatalytic activity in oxygen reduction reactions, as compared to their Au@Ag and Ag@Au core-shell counterparts, likely due to a synergistic effect between the gold cores and silver semishells that optimized oxygen binding to the nanoparticle surface.

Sensitive detection and glycoprofiling of a prostate specific antigen using impedimetric assays

This study presents a proof-of-concept for the development of an impedimetric biosensor for ultra-sensitive glycoprofiling of prostate specific antigen (PSA). The biosensor exhibits three unique characteristics: (1) analysis of PSA with limit of detection (LOD) down to 4 aM; (2) analysis of the glycan part of PSA with LOD down to 4 aM level and; (3) both assays (i.e., PSA quantification and PSA glycoprofiling) can be performed on the same interface due to label-free analysis.