Development and validation of a quantitative ELISA for the measurement of PSA concentration

Synergistic enhancement mediated sensitive SERS-based immunoassay of PSA using versatile PDMS@AgNPs@ZIF-67 biomimetic substrates

Among various biomimetic polymer materials, polydimethylsiloxane (PDMS) stands out as an ideal matrix for surface-enhanced Raman scattering (SERS) due to its unique intrinsic Raman signal and tenacity. In order to realize the precise detection of prostate-specific antigen (PSA), we proposed a sandwich-type SERS-active immunostructure composed of PDMS@silver nanoparticles (Ag NPs)@ZIF-67 biomimetic film as the immunosubstrate and gold nanorods (Au NRs) as immunoprobes. Due to the synergistic effect of electromagnetic enhancement facilitated by biomimetic surfaces and chemical enhancement achieved by ZIF-67, this structure enabled an ultrasensitive and selective detection of PSA across a broad range from 10-3 to 10-9 mg/mL. The achieved limit of detection was as low as 3.0 × 10-10 mg/mL. Particularly, the intrinsic Raman signal of PDMS matrix at 2905 cm-1 was employed as a potential internal standard (IS) in the detection, achieving a high coefficient of determination (R2) value of 0.996. This multifunctional SERS substrate-mediated immunoassay holds vast potential for early diagnosis of prostate cancer, offering promising prospects for clinical applications.

The synergistic effects of coupling Au nanoparticles with an alkynyl Co(II) phthalocyanine on the detection of prostate specific antigen

Prostate specific antigen (PSA) aptasensors are fabricated using a novel asymmetrically substituted Co phthalocyanine (CoPc), gold nanoparticles (AuNPs) and PSA-specific antigen. The fabricated aptasensors are: GCE-AuNPs-Aptamer, GCE@CoPc-Aptamer and GCE-AuNPs@CoPc-Aptamer (GCE = glassy carbon electrode). The fabricated sensors are characterized at each modification step to monitor the changes occurring at the sensor surface. Concentration studies were carried out using differential pulse voltammetry (DPV) and electrochemical impedance spectroscopy (EIS) to determine detection limits. All the fabricated aptasensors were found to be highly specific and selective but the GCE-AuNPs@CoPc-Aptamer nanoconjugate performed the best. The aptasensors were also tested in spiked serum samples and detection limits, as well as % recoveries were determined. The results obtained showed that the GCE-AuNPs@CoPc-Aptamer has the potential to be used for clinical studies as the results agree with those obtained for detection of PSA in buffer.

High Sensitivity Label-Free Quantitative Method for Detecting Tumor Biomarkers in Human Serum by Optical Microfiber Couplers

Label-free optical fiber immunosensors have attracted widespread attention in recent decades due to their high sensitivity. However, nonspecific adsorption in serum has remained a critical bottleneck in existing label-free fiber optic biosensors, which hinders their widespread use in diagnostics. In addition, individual differences in clinical human serum (HS) negatively impact biosensing results. In this work, the modified serum preadsorption strategy was applied to reduce nonspecific adsorption by forming a saturated antifouling interface on an optical microfiber coupler (OMC). Furthermore, to reduce the effect of the differences between individual HS samples, we proposed a new method where Sigma HS was used as a wavelength shift reference due to being close to clinical serum compared to other serums. Sigma HS was used first to reduce the differences in immune sensors before performing a clinical sample test in which quantitative detection was achieved based on the independent calibration of several sensors with wide dynamic ranges via dissociation processes. The individual differences in 25% HS were corrected by 30% Sigma HS. As a proof of concept, the label-free OMC immune sensor demonstrates good sensitivity and specificity for the detection of carcinoembryonic antigen (CEA) in 25% Sigma HS at different concentrations. The detection limit of CEA reached as low as 34.6 fg/mL (0.475 fM). Additionally, label-free quantitative detection of CEA using this OMC immune sensor was verified experimentally according to the calibration line, and the results agree well with clinical examination detection. To our knowledge, it is the first study to employ an OMC immune sensor in point-of-care label-free quantitative detection for clinical HS.

Development of site-specific antibody-conjugated immunoliposomes for sensitive detection of disease biomarkers

Liposome-based immunoassay (LIA) is an attractive protocol for amplifying the detection signals because of the excellent ability of liposomes to encapsulate signal marker compounds. The antigen-binding activity of the conjugated antibodies on the liposomal surface is crucial for the specificity and sensitivity of LIA. We present here a general platform to ensure that antibodies can conjugate onto the surface of liposomes in a site-specific and oriented manner. A His-handle-modified antibody with Fc region-specific and covalent conjugation was first fabricated using a photoactivatable Z_Bpa-His tag that was engineered using the aminoacyl-tRNA synthetase/suppressor tRNA technique. Based on the high affinity between the His tag and divalent metal ions, the novel His-modified antibody was oriented onto the surface of nickel ion-modified liposomes encapsulating horseradish peroxidase. With the prostate-specific antigen as a model, the detection efficiency of the new immunoliposomes was evaluated by chemiluminescence immunoassay. The immunoliposomes exhibited a limit of detection of 0.2 pg mL^-1, which was a six time improvement compared with that of the chemical-coupled antibody-liposome conjugates. Thus, the proposed immunoliposomes are expected to hold potential applications for the sensitive detection of various biomarkers in complicated serum samples.

Nanotechnology in Tumor Biomarker Detection: The Potential of Liganded Nanoclusters as Nonlinear Optical Contrast Agents for Molecular Diagnostics of Cancer

Cancer is one of the leading causes of premature death, and, as such, it can be prevented by developing strategies for early and accurate diagnosis. Cancer diagnostics has evolved from the macroscopic detection of malignant tissues to the fine analysis of tumor biomarkers using personalized medicine approaches. Recently, various nanomaterials have been introduced into the molecular diagnostics of cancer. This has resulted in a number of tumor biomarkers that have been detected in vitro and in vivo using nanodevices and corresponding imaging techniques. Atomically precise ligand-protected noble metal quantum nanoclusters represent an interesting class of nanomaterials with a great potential for the detection of tumor biomarkers. They are characterized by high biocompatibility, low toxicity, and suitability for controlled functionalization with moieties specifically recognizing tumor biomarkers. Their non-linear optical properties are of particular importance as they enable the visualization of nanocluster-labeled tumor biomarkers using non-linear optical techniques such as two-photon-excited fluorescence and second harmonic generation. This article reviews liganded nanoclusters among the different nanomaterials used for molecular cancer diagnosis and the relevance of this new class of nanomaterials as non-linear optical probe and contrast agents.

Electrochemiluminescent determination of prostate-specific antigen using Au@(MoS2/GO/o-MWNTs) nanohybrids as co-reaction accelerator and hyperbranched hybridization chain reaction for signal amplification

Three-dimensional flowerlike Au@(MoS₂/GO/o-MWNTs) nanohybrids (abbreviated as AMGMs) were synthesized and then introduced into an electrochemiluminescence (ECL) system as a new co-reaction accelerator for the ultrasensitive prostate-specific antigen (PSA). The AMGMs not only served as a substrate with good conductivity and a large specific surface area for loading abundant primary antibodies but also acted as an effective co-reaction accelerator; the co-reaction accelerator could interact with a co-reactant rather than the luminophore to boost the generation of free radical intermediates, thereby producing abundant excited states of luminophores to amplify the ECL signal response. Additionally, an anticipated signal amplification strategy based on the hybridization chain reaction (HCR) was developed by gathering a large amount of a DNA initiator on gold nanoparticles. These gathered DNA initiators could generate multiple DNA concatemers and attach more signal molecules, which resulted in outstanding exponential signal amplification. Consequently, the ECL immunosensor demonstrated high sensitivity, with a linear range from 0.1 pg mL^-1 to 50 ng mL^-1 and a detection limit of 0.028 pg mL^-1. In addition, the immunosensor displayed excellent stability and selectivity. It was evaluated by analyzing human serum sample. The recovery obtained was 98.80-112.00% and the RSD was 1.73-3.12%, indicating the immunosensor could be applied to the simultaneous detection of PSA in human serum samples. Graphical abstract.

The electrochemical detection of prostate specific antigen on glassy carbon electrode modified with combinations of graphene quantum dots, cobalt phthalocyanine and an aptamer

Herein, a novel aptasensor is developed for the electrochemical detection of prostate specific antigen (PSA) on electrode surfaces modified using various combinations of a Cobalt phthalocyanine (CoPc), an aptamer and graphene quantum dots (GQDs). Electrochemical impedance spectroscopy (EIS) as well as differential pulse voltammetry (DPV) are employed for the detection of PSA. In both analytical techniques, linear calibration curves were observed at a concentration range of 1.2-2.0 pM. The glassy carbon electrode where CoPc and GQDs are placed on the electrode when non-covalently linked followed by addition of the aptamer (GQDs-CoPc(ππ)-aptamer (sequential)) showed the best performance with a limit of detection (LoD) as low as 0.66 pM when using DPV. The detection limits were much lower than the dangerous levels reported for PSA in males tested for prostate cancer. This electrode showed selectivity for PSA in the presence of bovine serum albumin, glucose and L-cysteine. The aptasensor showed good stability, reproducibility and repeatability, deeming it a promising early detection device for prostate cancer.

An enhanced centrifugation-assisted lateral flow immunoassay for the point-of-care detection of protein biomarkers

Protein biomarkers are widely used for disease diagnosis, but the current detection methods utilized in centralized laboratories are mainly based on enzyme-linked immunosorbent assay (ELISA)-derived sandwich-type immunoassays such as chemiluminescent or electrochemiluminescent immunoassays, which suffer from long detection times and cumbersome instruments. For the point-of-care (POC) detection of protein biomarkers, various test strips for lateral flow immunoassay (LFIA) have been manufactured, but their detection sensitivities and capabilities for raw samples are limited. In this study, an enhanced centrifugation-assisted lateral flow immunoassay (ECLFIA) was established to rapidly detect protein biomarkers in whole blood with a higher sensitivity than LFIA. By inserting a nitrocellulose membrane into a centrifugal disc, fully automated operations, including sample preparation, active lateral flow actuation, washing, and signal amplification, which could hardly be performed in conventional LFIA, were enabled on the centrifugal platform for ECLFIA. The entire process for detecting human prostate specific antigen (PSA) in a drop of blood (20 μL) could be completed in 15 min. The limit of detection for our ECLFIA system was 0.028 ng mL^-1, showing a 21.4-fold improvement compared to that of LFIA. Moreover, this system was utilized to detect PSA in 34 clinical samples. The results were compared to those measured using a commercial instrument used in the hospital, and a good correlation coefficient of 0.986 was obtained, demonstrating the practicality of this ECLFIA system. In summary, the ECLFIA system established in this study can be an efficient tool for the POC detection of protein biomarkers with comprehensive advantages in sensitivity, simplicity and speed.

Application of various optical and electrochemical aptasensors for detection of human prostate specific antigen: A review

Early stage detection of prostate cancer, one of the main causes of mortality among men, is of great importance for better treatment of the patients. Prostate specific antigen (PSA) is a glycoprotein which has been considered as the most potential serological biomarker for the detection of prostate cancer. Among the various techniques employed for PSA detection, aptamer-based biosensors (aptasensors) have achieved notable attention because of their unique features and great potentials as diagnostic tools. A variety of strategies such as integration of nanomaterials (NMs) into the structure of aptasensors have also been applied for enhancing the sensitivity of PSA detection. This article reviews recent advances in various optical and electrochemical aptasensors used for PSA detection.

High-Performance All-Inorganic CsPbCl3 Perovskite Nanocrystal Photodetectors with Superior Stability

All-inorganic perovskites nanostructures, such as CsPbCl₃ nanocrystals (NCs), are promising in many applications including light-emitting diodes, photovoltaics, and photodetectors. Despite the impressive performance that was demonstrated, a critical issue remains due to the instability of the perovskites in ambient. Herein, we report a method of passivating crystalline CsPbCl₃ NC surfaces with 3-mercaptopropionic acid (MPA), and superior ambient stability is achieved. The printing of these colloidal NCs on the channel of graphene field-effect transistors (GFETs) on solid Si/SiO₂ and flexible polyethylene terephthalate substrates was carried out to obtain CsPbCl₃ NCs/GFET heterojunction photodetectors for flexible and visible-blind ultraviolet detection at wavelength below 400 nm. Besides ambient stability, the additional benefits of passivating surface charge trapping by the defects on CsPbCl₃ NCs and facilitating high-efficiency charge transfer between the CsPbCl₃ NCs and graphene were provided by MPA. Extraordinary optoelectronic performance was obtained on the CsPbCl₃ NCs/graphene devices including a high ultraviolet responsivity exceeding 10⁶ A/W, a high detectivity of 2 × 10¹³ Jones, a fast photoresponse time of 0.3 s, and ambient stability with less than 10% degradation of photoresponse after 2400 h. This result demonstrates the crucial importance of the perovskite NC surface passivation not only to the performance but also to the stability of the perovskite optoelectronic devices.

A Novel Gold Nanoprobe for a Simple Electrochemiluminescence Determination of a Prostate-specific Antigen Based on a Peptide Cleavage Reaction

A novel gold nanoprobe for a sensitive and simple determination of a prostate-specific antigen (PSA) was designed on the basis of homogeneous detection and a peptide cleavage reaction. The gold nanoprobe (AuNPs-peptide-Ru1) consisted of a specific peptide tagged with a ruthenium(II) complex (Ru1) and gold nanoparticles (AuNPs) conjugated with the peptide via the strong Au-S bond between the AuNPs surface and the thiol group of the peptide. The electrochemiluminescence (ECL) enzymatic-cleavage-reaction-based bioanalytic system based on homogeneous detection has overcome shortcomings from a complicated fabrication process of traditional electrodes. In the presence of the target PSA, it specifically cleaved the peptide of the AuNPs-peptide-Ru1, and the ECL signal substance (Ru1) part dissociated from AuNPs-peptide-Ru1. This resulted in an increase in the ECL intensity. The ECL biosensor could detect PSA concentrations in the range from 1.0 × 10^-12 to 1.0 × 10^-9 g/mL, the detection limit was 4.0 × 10^-13 g/mL. The assay with the advantages of a simple method for PSA was selective and fast. It is superior to the immunoassay, and is a promising strategy to develop biosensors based on enzymatic cleavage including electrochemistry and optics.

Using a glucose meter to quantitatively detect disease biomarkers through a universal nanozyme integrated lateral fluidic sensing platform

Along with the advance in medical research, more biomarkers emerge as useful indicators for both disease and health index. However, majority of them have no practical or economic testing methods available yet, or rely on high-costing methods such as Enzyme-Linked Immuno-Sorbent Assay (ELISA), High-Performance Liquid Chromatography (HPLC), Mass Spectrum, and immunohistochemistry (IHC). In this article, we develop a universal nanozyme integrated testing platform for biological molecules that incorporates the electrochemical measurement of glucose with lateral flow immunostrip (LFS) for target analytes. This design involves the quantitative conversion of analytes into invertase and then glucose, which can be measured by an extremely affordable meter. The feasibility of this design was validated using 8-hydroxy-2'-deoxyguanosine (8-OHdG) and prostate specific antigen (PSA) as representatives for small molecules and moderate to large proteins respectively. Our approach yields results comparable to commercial diagnostic ELISA kits at a substantially reduced cost and reaction time. Specifically, the design has a detection limit of 0.23 ng mL^-1 for 8-OHdG and 1.26 ng mL^-1 for PSA, and a detection range of 0.1-100 ng mL^-1 for 8-OHdG and 1-100 ng mL^-1 for PSA. By combining the accessibility of well-established glucose testing and LFS, our design can serve as a point of care testing method that can be fully integrated into the personal lifestyle without requiring professional assistance.

Selected landscape phage probe as selective recognition interface for sensitive total prostate-specific antigen immunosensor

The level of total prostate-specific antigen (t-PSA) is generally known as the key index of prostate cancer. Here, phage probes against t-PSA were selected from f8/8 landscape phage library. After three rounds of biopanning, four t-PSA-binding phage clones were isolated and identified by the DNA sequencing. Based on the phage capture assay, the phage clone displaying the fusion peptide ATRSANGM showed highest affinity and specificity against t-PSA. Subsequently, the t-PSA-specific phage was used as t-PSA capture probe in a sandwich enzyme-linked immunosorbent assay (ELISA) and differential pulse voltammetry (DPV) assay systems. Both assay methods showed high specificity and acceptable reliability for real serum samples analysis. By comparison, DPV method showed wider linear range (0.01-100 ng mL^-1) and lower limit of detection (3 pg mL^-1) than those (3.3-330 ng mL^-1 and 1.6 ng mL^-1) of ELISA. Moreover, DPV system showed smaller distinction to the authoritative method in real samples assay. Excitingly, the phage probe based DPV immunosensor showed high sensitivity for the detection of t-PSA and LOD achieved the pg mL^-1 level, which was far lower than those values (usually above 0.1 ng mL^-1) for reported immunosensors based on antibodies. Due to the biocompatibility, multivalency, stability, and high structural homogeneity, the t-PSA-specific landscape phage demonstrates as a novel specific interface in biosensors.

Target-activatable gold nanoparticle-based aptasensing for protein biomarkers using stimuli-responsive aggregation

An ultrasensitive and selective light-scattering (LS) aptasensor for prostate specific antigen (PSA) was developed based on bifunctional DNA decorated gold nanoparticles (Au NPs) by use of target stimuli-responsive assembly. Both binding sequence poly adenine (poly(dA), Domain I) and the recognition sequence aptamer (Domain II) of bifunctional ssDNA were in favor of the sensitivity for the fabricated light-scattering aptasensor due to modulated the lateral spacing of DNA on Au NPs surface and possessed strong antigen binding affinity, respectively. And they efficiently promoted the Au NPs aggregation and activated the signal of light-scattering of aptasensor. The formation of aptamer-PSA complex induced conformational transformation of the aptamer on the surface of the Au NPs-based aptasensor and then tuned the interparticle distance of gold nanoparticle assemblies. The larger scattering particles, the higher light-scattering intensity. Target stimuli-responsive aggregation behavior of Au NPs lit up the light-scattering signal of aptasensor. As the concentration of PSA increased, the light-scattering intensity gradually enhanced. The aptasensor response for PSA detection was in the linear range from 0.01 ng/mL to 20 ng/mL with the detection limit of 2 pg/mL. The thiol-free Au NPs-based light-scattering aptasensor has exceptional performances with ultrasensitivity and high selectivity besides the advantage of economic and facile fabrication. Moreover, the proposed target-activated aptasensor was applied for the detection of PSA in serum samples and demonstrated great potential in clinical applications.

A comparative Study of Aptasensor Vs Immunosensor for Label-Free PSA Cancer Detection on GQDs-AuNRs Modified Screen-Printed Electrodes

Label-free and sensitive detection of PSA (Prostate Specific Antigen) is still a big challenge in the arena of prostate cancer diagnosis in males. We present a comparative study for label-free PSA aptasensor and PSA immunosensor for the PSA-specific monoclonal antibody, based on graphene quantum dots-gold nanorods (GQDs-AuNRs) modified screen-printed electrodes. GQDs-AuNRs composite has been synthesized and used as an electro-active material, which shows fast electron transfer and catalytic property. Aptamer or anti-PSA has immobilized onto the surface of modified screen printed electrodes. Three techniques are used simultaneously, viz. cyclic voltammetry (CV), differential pulse voltammetry (DPV) and electrochemical impedence spectroscopy (EIS) to investigate the analytical performance of both PSA aptasensor and PSA immunosensor with its corresponding PSA antigen. Under optimum conditions, both sensors show comparable results with an almost same limit of detection (LOD) of 0.14 ng mL-1. The results developed with aptasensor and anti-PSA is also checked through the detection of PSA in real samples with acceptable results. Our study suggests some advantages of aptasensor in terms of better stability, simplicity and cost effectiveness. Further our present work shows enormous potential of our developed sensors for real application using voltammetric and EIS techniques simultaneous to get reliable detection of the disease.

Highly sensitive immunosensing of prostate specific antigen using poly cysteine caped by graphene quantum dots and gold nanoparticle: A novel signal amplification strategy

A mediator-free electrochemical immunosensor for quantitation of prostate specific antigen (PSA) based on dual signal amplification strategy was fabricated. In this work, PSA-antibody (anti-PSA) was immobilized onto a green and biocompatible nanocomposite containing poly l-cysteine (P-Cys) as conductive matrix and graphene quantum dots (GQDs)/gold nanoparticles (GNPs) as dual signal amplification elements. Therefore, a novel multilayer film based on P-Cys, GQDs, and GNPs was exploited to develop a highly sensitive amperometric immunosensor for detection of PSA. Fully electrochemical methodology was used to prepare a new transducer on a gold surface which provided a high surface area to immobilize a high amount of the anti-PSA. Importantly, GNPs prepared by soft template synthesized method lead to compact morphology was achieved. The surface morphology of electrode surface was characterized by high-resolution field emission scanning electron microscope (FE-SEM) and energy dispersive spectroscopy (EDX). Chemical compositions of the gold nanoparticles were analysed by an EDX. The immunosensor was employed for the detection of PSA in physiological pH. Under optimized condition the calibration curve for PSA concentration was linear up to 2-9pgmL^-1 with lower limit of quantification of 1.8pgmL^-1.

Target-triggered signal turn-on detection of prostate specific antigen based on metal-enhanced fluorescence of Ag@SiO2@SiO2-RuBpy composite nanoparticles

A three-layer core-shell nanostructure consisting of a silver core, a silica spacer, and a fluorescent dye RuBpy-doped outer silica layer was fabricated, and the optimal metal-enhanced fluorescence (MEF) distance was explored through adjusting the thickness of the silica spacer. The results show that the optimal distance is ∼10.4 nm with the maximum fluorescence enhancement factor 2.12. Then a new target-triggered MEF 'turn-on' strategy based on the optimized composite nanoparticles was successfully constructed for quantitative detection of prostate specific antigen (PSA), by using RuBpy as the energy donor and BHQ-2 as the acceptor. The hybridization of the complementary DNA of PSA-aptamer immobilized on the surface of the MEF nanoparticles with PSA-aptamer modified with BHQ-2, brought BHQ-2 in close proximity to RuBpy-doped silica shell and resulted in the decrease of fluorescence. In the presence of target PSA molecules, the BHQ-PSA aptamer is dissociated from the surface of the nanoparticles with the fluorescence switched on. Therefore, the assay of PSA was achieved by measuring the varying fluorescence intensity. The results show that PSA can be detected in the range of 1-100 ng ml^-1 with a detection limit of 0.20 ng ml^-1 (6.1 pM), which is 6.7-fold increase of that using hollow RuBpy-doped silica nanoparticles. Moreover, satisfactory results were obtained when PSA was detected in 1% serum.

SERS-based immunoassay on 2D-arrays of Au@Ag core–shell nanoparticles: influence of the sizes of the SERS probe and sandwich immunocomplex on the sensitivity

The sensitivity of immunoassay performed on SERS-active substrates can be improved by optimizing the size of SERS probes and also by decreasing the size of sandwich immunocomplex.

Label-free electrochemical aptasensing of the human prostate-specific antigen using gold nanospears

Gold nanospears were electrodeposited with the assistance of arginine as a soft template and precise selection of experimental parameters. The nanospears were then employed as a transducer to immobilize an aptamer of prostate-specific antigen (PSA) and fabrication of a label-free electrochemical aptasensor. The aptasensor was employed for the detection of PSA with a linear concentration range of 0.125-200ngmL(-1) and a limit of detection of 50pgmL(-1). The aptasensor was successfully applied to detect PSA in blood serum samples of healthy and patient persons.

A new strategy for label-free electrochemical immunoassay based on "gate-effect" of β-cyclodextrin modified electrode

A novel label-free electrochemical immunoassay was developed for prostate-specific antigen (PSA) detection via using β-cyclodextrin (β-CD) assembled layer created gates for the electron transfer of probe. To construct the sensor, a gold electrode was self-assembled with monoclonal anti-PSA antibody labeled 6-mercapto-β-cyclodextrin. Interspaces among β-CD molecules in the layer were automatically formed on gold electrode, which act as the channel of the electron transfer of [Fe(CN)6](3-/4-) probe. When PSA bind with anti-PSA, it can block these channels on the electrode surface due to their steric hindrance effect, resulting in the decrease in redox current of the probe. Through such a gate-controlled effect, ultra trace amount of PSA may make the currents change greatly after the immunoreaction, which enhanced the signal-to-noise ratio to achieve the amplification effect. By evaluating the logarithm of PSA concentrations, the immunosensor had a good linear response to the current changes with a detection limit of 0.3 pg/mL (S/N = 3) when PSA concentration ranged from 1.0 pg/mL to 1.0 ng/mL. The label-free immunosensor exhibited satisfactory performances in sensitivity, repeatability as well as specificity.

Acoustic micromixing increases antibody-antigen binding in immunoassays

Sound wave-assisted acoustic micromixing has been shown to increase the binding of molecules in small volumes (10-100 μL) where effective mixing is difficult to achieve through conventional techniques. The aim of this work is to study whether acoustic micromixing can increase the binding efficiency of antibodies to their antigens, a reaction that forms the basis of immunoassays, including enzyme-linked immunosorbent assay (ELISA). Using a procedure from a general ELISA and immobilizing an antigen on wells of 96-well plates, it was found that acoustic micromixing at 125-150 Hz increased the initial rate of antibody-antigen binding by over 80 % and the total binding at the end point (i.e., 45 min) by over 50 %. As a result, acoustic micromixing achieved a binding level in 9 min that would otherwise take 45 min on a standard platform rocking mixer. Therefore acoustic micromixing has the potential to increase the detection sensitivity of ELISA as well as shorten the antigen-antibody binding times from typically 45-60 min to 15 min.

Sub-5 nm lanthanide-doped lutetium oxyfluoride nanoprobes for ultrasensitive detection of prostate specific antigen

It remains challenging to develop ultrasmall (<5 nm) but highly luminescent bioprobes with a large linear detection range for the early diagnosis and monitoring of prostate cancer (PCa). Benefiting from the high molar density of lanthanide ions in an oxyfluoride matrix and the superior dissolution capability of Lu₆O₅F₈ nanoparticles in the enhancer solution, we demonstrated the successful use of novel sub-5 nm Lu₆O₅F₈:Eu³⁺ nanoprobes for the detection of prostate specific antigen (PSA) in clinical serum samples. The limit of detection for PSA is as low as 0.52 pg mL^-1, which is almost a 200-fold improvement relative to that of a commercial dissociation-enhanced lanthanide fluoroimmunoassay (DELFIA) kit. The PSA levels detected in 23 patient serum samples were consistent with those measured independently by the DELFIA kit, showing the assay's reliability with a correlation coefficient of 97%. A linear range of 4 orders of magnitude ranging from 8.5 × 10^-4 to 5.6 ng mL^-1 for the assay of PSA was achieved, which is highly promising for the early diagnosis of PCa and monitoring of PCa relapse of patients after radical prostatectomy.

In situ generation of electron acceptor to amplify the photoelectrochemical signal from poly(dopamine)-sensitized TiO2 signal crystal for immunoassay

A photoelectrochemical protocol was designed for quantitative monitoring of tumor markers by utilizing poly(dopamine)-sensitized TiO₂ signal crystal.

Biomarker detection technologies and future directions

Biomarkers play a vital role in disease detection and treatment follow-up. It is important to note that diseases in the early stage are typically treated with the greatest probability of success. However, due to various technical difficulties in current technologies for the detection of biomarkers, the potential of biomarkers is not explored completely. Therefore, the developments of technologies, which can enable the accurate detection of prostate cancer at an early stage with simple, experimental protocols are highly inevitable. This critical review evaluates the current methods and technologies used in the detection of biomarkers. The aim of this article is to provide a comprehensive review covering the advantages and disadvantages of the biomarker detection methods. Future directions for the development of technologies to achieve highly selective and sensitive detection of biomarkers for point-of-care applications are also commented on.

Detection of protein biomarker using a blood glucose meter

mHeath technologies are recognized to play important roles in the future of personal care and medicine. However, their full potentials have not been reached, as most of current technologies are restricted to monitoring physical and behavioral parameters, such as body temperature, heart rate, blood pressure, and physical movement, while direct monitoring of biomarkers in body fluids can provide much more accurate and useful information for medical diagnostics. A major barrier to realizing the full potential of mHealth is the high costs and long cycles of developing mHealth devices capable of monitoring biomarkers in body fluids. To lower the costs and shorten the developmental cycle, we have demonstrated the leveraging of the most successful portable medical monitoring device on the market, the blood glucose meter (BGM), with FDA-approved smartphone technologies that allow for wireless transmission and remote monitoring of a wide range of non-glucose targets. In this protocol, an aptamer-based assay for quantification of interferon-γ (IFN-γ) using an off-the-shelf BGM is described. In this assay, an aptamer-based target recognition system is employed. When IFN-γ binds to the aptamer, it triggers the release of a reporter enzyme, invertase, which can catalyze the conversion of sucrose (not detected by BGM) to glucose. The glucose being produced is then detected using a BGM. The system mimics a competitive enzyme-linked immunosorbent assay (ELISA), where the traditional immunoassay is replaced by an aptamer binding assay; the reporter protein is replaced by invertase, and finally the optical or fluorescence detector is replaced with widely available BGMs.

Development of an ELISA for the Pharmacokinetic Evaluation of a Murine Anti CD66 Monoclonal Antibody in Human Serum

An enzyme-linked immunosorbent assay (ELISA) was needed to assist in the pharmacokinetic evaluation of the murine antibody conjugate CHX A" DTPA Besilesomab in serum samples in a clinical trial . A search failed to locate a validated assay that quantified murine antibodies in human serum so the purpose of this article was to develop a robust assay, validated against current guidelines. A detailed method for an ELISA to measure a murine antibody in human serum is described. The assay was validated as fit for purpose against the target values of coefficient of variation < 20% and accuracy ± 20%.

Gel pad array chip for high throughput and multi-analyte microbead-based immunoassays

We present here a gel pad array chip for high-throughput and multi-analyte microbead-based immunoassays. The chip is fabricated by photo-patterning of two polymeric gels, polyacrylamide gel and polyethylene glycol (PEG) gel, on a glass slide. The resulting chip consists of 40 polyacrylamide gel pad array units for the immobilization of microbeads and each gel pad array is surrounded with a PEG micropillar ring to confine the samples within the microarray. As a proof of concept, this chip was tested for quantitative immunoassays for two model cancer markers, human chorionic gonadotropin (hCG) and prostate specific antigen (PSA), in serum samples. Detection limits below the physiological threshold level for cancer diagnosis were achieved with good inter- and intra-chip reproducibility. Moreover, by using spatial encoded microbeads, simultaneous detection of both hCG and PSA on each gel pad array is achieved with single filter fluorescence imaging. This gel pad array chip is easy to use, easy to fabricate with low cost materials and minimal equipment and reusable. It could be a useful tool for common biolabs to customize their own microbead array for multi-analyte immunoassays.

Rapid aptasensor capable of simply diagnosing prostate cancer

Using guanine (G)-rich DNA aptamer-conjugated 6-carboxyfluorescein (6-FAM) capable of rapidly capturing prostate specific antigen (PSA) in human serum, cost-effective and simple biosensor with guanine chemiluminescence detection was developed for early diagnosis of prostate cancer. Free G-rich DNA aptamer-conjugated 6-FAM emits bright light in guanine chemiluminescence reaction based on the principle of chemiluminescent resonance energy transfer (CRET). However, G-rich DNA aptamer-conjugated 6-FAM bound with PSA cannot emit light because PSA acts as a strong interference in CRET between 6-FAM and high-energy intermediate formed from the reaction of 3,4,5-trimethoxylphenylglyoxal (TMPG) and guanine of G-rich DNA aptamer. A chemiluminescent biosensor, developed using the different properties of G-rich DNA aptamer-conjugated 6-FAM in the absence and presence of PSA in guanine chemiluminescence reaction, was able to quantify trace levels of PSA in human serum within 30 min without time-consuming and complicated procedures (e.g., multiple incubation and washings) required for conventional immunoassays operated with expensive and intractable antibodies. The limit of detection of chemiluminescent biosensor having a wide linear dynamic range (1.9-125 ng/ml) was 1.0 ng/ml. The excellent correlation (R=0.985) between chemiluminescent biosensor and conventional enzyme immunoassay indicates that the accurate, precise, and rapid chemiluminescent biosensor can be applied as a new method for early diagnosis of prostate cancer.

Recent progress in prostate-specific antigen and HIV proteases detection

Proteases mediate a wide variety of biological events and have a critical role in the development of many diseases. Protease detection methods can be hindered by the limitation of assay safety, sensitivity, specificity, time constraints and ease of on-site analysis. Notably, the implementation of various detection methods on biosensing platforms translates them into practical biosensing applications. Currently, the detection of prostate cancer and AIDS at the earliest occasion is one of the major research obstacles. Therefore, recent advances focus on the development of portable detection systems toward point-of-care testing. These detection systems should be highly sensitive and specific for the detection of their prognostic biomarkers, such as the prostate-specific antigen and HIV load assay for prostate cancer and AIDS, respectively. These methods will also facilitate decision-making on a treatment regimen.

Association of cadmium and lead with antioxidant status and incidence of benign prostatic hyperplasia in patients of Western India

The association of cadmium (Cd) and lead (Pb) in the pathophysiology and progression of benign prostate hyperplasia (BPH) has been evaluated in an epidemiological study with 116 BPH patients of the western part of India. The prostatic acid phosphatase activity, prostate-specific antigen, maximum urinary flow rate (Q max), and redox status of BPH patients were correlated with Cd and Pb contents. Additionally, patients were also separated on the basis of their age, genetic lineage, and additive habits and correlated with the Cd, Pb, and Q max levels. Our results suggest that the accumulation of toxic metals in prostate tissue has a significant positive correlation with the pathogenesis of BPH. Cd and Pb exert their effects through altered antioxidant defense mechanisms, ultimately leading to increased BPH severity. Progression of the pathogenesis also depends on other factors such as additive habits, genetic lineage, and age of the patients.