A reusable electrochemical immunosensor fabricated using a temperature-responsive polymer for cancer biomarker proteins

Toward a Plasmon-Based Biosensor throughout a Thermoresponsive Hydrogel

This study investigates the potential of thermoresponsive hydrogels as innovative substrates for future in vitro diagnostic (IVD) applications using AVAC technology, developed and patented by the Mecwins biomedical company. In order to convert the hydrogel in a substrate compatible with AVAC technology, the following prerequisites were established: (1) the hydrogel layer needs to be permeable to gold nanoparticles (AuNPs), and (2) the optical properties of the hydrogel should not interfere with the detection of AuNPs with AVAC technology. These two key aspects are evaluated in this work. A silicon substrate (Sil) was coated with a layer of a thermosensitive hydrogel (TSH) based on poly(N-isopropylacrylamide-co-N,N'-methylene bis(acrylamide) (PNIPAAm-co-MBA). The TSH offers the advantage of easy modulation of its porosity through cross-linker adjustments, crucial for the plasmonic nanoparticle (NP) permeation. The platforms, denominated as (Sil)-g-(PNIPAAm-co-MBA), were fabricated by changing the cross-linker concentrations and exploring three deposition methods: drop casting (DC), spin coating (SC), and 3D printing (3D); the DC approach resulted in a very homogeneous and thin hydrogel layer, very suitable for the final application. Furthermore, after physical-chemical characterization, the TSH demonstrated its functionality in regulating nanoparticle absorption, and AVAC technology's capability to precisely identify such NPs through the hydrogel matrix was validated. The proposed hydrogel platform fulfills the initial requirements, opening the possibility for employing these hydrogels as dynamic substrates in sandwich immunoassay devices. The next step in the development of the hydrogel substrate would be its functionalization with biorecognition groups to allow for biomarker detection. By leveraging their enhanced capture efficiency and the ability to manipulate particle flow thermally, we anticipate a significant advancement in diagnostic methodologies, combining the spatial benefits of three-dimensional hydrogel structures with the precision of AVAC's digital detection.

Highly Reusable Electrochemical Immunosensor for Ultrasensitive Protein Detection

The detection and quantification of protein biomarkers in bodily fluids is important for many clinical applications, including disease diagnosis and health monitoring. Current techniques for ultrasensitive protein detection, such as enzyme-linked immunosorbent assay (ELISA) and electrochemical sensing, involve long incubation times (1.5-3 hr) and rely on single-use sensing electrodes which can be costly and generate excessive waste. This work demonstrates a reusable electrochemical immunosensor employing magnetic nanoparticles (MNPs) and dually labeled gold nanoparticles (AuNPs) for ultrasensitive measurements of protein biomarkers. As proof of concept, this platform was used to detect C-X-C motif chemokine ligand 9 (CXCL9), a biomarker associated with kidney transplant rejection, immune nephritis from checkpoint inhibitor therapy, and drug-associated acute interstitial nephritis, in human urine. The sensor successfully detected CXCL9 at concentrations as low as 27 pg/mL within ~1 hr. This immunosensor was also adapted onto a handheld smartphone-based diagnostic device and used for measurements of CXCL9, which exhibited a lower limit of detection of 65 pg/mL. Lastly, we demonstrate that the sensing electrodes can be reused for at least 100 measurements with a negligible loss in analytical performance, reducing the costs and waste associated with electrochemical sensing.

Electrochemical immunosensor based on titanium dioxide grafted MXene for EpCAM antigen detection

This study proposes the fabrication of a highly sensitive electrochemical immunosensor for label-free detection of EpCAM antigen. MXenes, novel 2D materials have become popular owing to their unique electrochemical properties. Unlike conventional immunosensors, which are unable to detect the carcinoma at primary stage and also time consuming, the use of highly conducting MXene provides a label-free and highly sensitive immunosensor. Herein, we develop a unique immunosensor, which is based on the in-situ growth of 2D-TiO2 onto the novel 2D-Ti3C2Tx sheets by hydrothermal treatment. The 2D/2D TiO2/Ti3C2Tx hybrid provides a platform having a large effective surface area, and more number of electrochemically active sites to enhance the electron transfer rate through the redox probe. The designed sensing platform, BSA/anti-EpCAM/TiO2/Ti3C2Tx@ITO shows a broad linear range (1 ag/mL to 10 ng/mL) with high sensitivity (6.661 µA ag-1 mL cm-2), and low detection limit (0.7 ag/mL) for EpCAM antigen detection under optimized conditions. The proposed immunosensor possesses good reproducibility, long-term stability, and outstanding selectivity and specificity. Moreover, the clinical applicability of the novel immunosensor is tested in spiked human serum showing good recovery.

Fabrication of a reusable electrochemical platform based on acid-responsive host-guest interaction with β- cyclodextrin

A reusable electrochemical glassy carbon electrode (GCE) platform based on the acid-responsive host-guest interaction between β-cyclodextrin (β-CD) and benzimidazole (BM) derivatives was developed. The β-CD can specifically recognize the BM derivative through the acid -responsive host-guest interaction. The electrode was first modified by eletrografting to immobilize a diamine linker (Boc-EDA), resulting in GCEBoc-EDA in which one amine was used for covalent immobilization to the electrode and another Boc protected amine was used to solid-phase synthesis on following step-by-step modifications on the electrode. After deprotection of the Boc group on the GCEBoc-EDA, carbonyldiimidazole (CDI)-activated β-CD was coupled with -NH2 on the electrode to result in GCEβ-CD. Due to the nonspecific interaction, we further improved the GCEβ-CD electrode by introducing immobilized poly(ethylene glycol) methyl ether (PEG-Me) to result in GCEβ-CD/PEG-Me, along with optimized procedures. CV, DPV, and EIS methods were applied for recording the electrochemistry signals. We utilized GCEβ-CD/PEG-Me to investigate the host-guest interaction and found the electrochemical signal exhibited dynamic behavior. The GCEβ-CD/PEG-Me was able to regenerate the β-CD surface more than 20 times after HCl acidic washes. We further investigated the interaction of carbendazim (CBZ), a commonly used fungicide in the agriculture and food industry, and observed a positive electrochemical response. The sensor design has potential applications in ensuring food safety.

Point-of-Care Prostate Specific Antigen Testing: Examining Translational Progress toward Clinical Implementation

Prostate cancer (PCa) is the second most common male cancer and is attributable to over 375,000 deaths annually. Prostate specific antigen (PSA) is a key biomarker for PCa and therefore measuring patient PSA levels is an important aspect of the diagnostic pathway. Automated immunoassays are currently utilized for PSA analysis, but they require a laboratory setting with specialized equipment and trained personnel. This results in high diagnostic costs, extended therapeutic turnaround times, and restrictions on testing capabilities in resource-limited settings. Consequently, there is a strong drive to develop point-of-care (PoC) PSA tests that can offer accurate, low-cost, and rapid results at the time and place of the patient. However, many emerging PoC tests experience a trade-off between accuracy, affordability, and accessibility which distinctly limits their translational potential. This review comprehensively assesses the translational advantages and limitations of emerging laboratory-level and commercial PoC tests for PSA determination. Electrochemical and optical PSA sensors from 2013 to 2023 are systematically examined. Furthermore, we suggest how the translational potential of emerging tests can be optimized to achieve clinical implementation and thus improve PCa diagnosis globally.

Microfluidic Technology, Artificial Intelligence, and Biosensors As Advanced Technologies in Cancer Screening: A Review Article

Cancer screening techniques aim to detect premalignant lesions and enable early intervention to delay the onset of cancer while keeping incidence constant. Technology advancements have led to the development of powerful tools such as microfluidic technology, artificial intelligence, machine learning algorithms, and electrochemical biosensors to aid in early cancer detection. Non-invasive cancer screening methods like virtual colonoscopy and endoscopic ultrasonography have also been developed to provide comprehensive pictures of organs and detect cancer early. This review article provides an overview of recent advances in cancer screening in microfluidic technology, artificial intelligence, and biomarkers through a narrative literature search. Microfluidic devices enable easy handling of sub-microliter volumes and have become a promising tool for cancer detection, drug screening, and modeling angiogenesis and metastasis in cancer research. Machine learning and artificial intelligence have shown high accuracy in oncology-related diagnostic imaging, reducing the manual steps in lesion detection and providing standardized and accurate results, with potential for global standardization in areas like colon polyps, breast cancer, and primary and metastatic brain cancer. A biomarker-based cancer diagnosis is promising for early detection and effective therapy, and electrochemical biosensors integrated with nanoparticles offer multiplexing and amplification capabilities. Understanding these advanced technologies' basics, achievements, and challenges is crucial for advancing their use in oncology.

Current Update on Biomarkers for Detection of Cancer: Comprehensive Analysis

Early and effective diagnosis of cancer is decisive for its proper management. In this context biomarker-based cancer diagnosis is budding as one of the promising ways for early detection, disease progression monitoring, and effective cancer therapy. Integration of Biosensing devices with different metallic/nonmetallic nanoparticles offers amplification and multiplexing capabilities for simultaneous detection of cancer biomarkers (CB's). This study provides a comprehensive analysis of the most recent designs and fabrication methodologies designed for developing electrochemical biosensors (EB) for early detection of cancers. The role of biomarkers in cancer therapeutics is also discussed.

Gold-silver alloy film based surface plasmon resonance sensor for biomarker detection

In this study, we developed a gold‑silver alloy film based surface plasmon resonance (AuAg-SPR) sensor with wavelength interrogation to detect cancer antigen 125 (CA125) using a sandwich immunoassay. We first theoretically simulated the sensitivity of conventional gold film based SPR (Au-SPR) sensor and AuAg-SPR sensor, and conducted a series of experiments to investigate the sensitive characteristics of AuAg-SPR sensor, including the angle and refractive index (RI) sensitivity. We then conducted CA125 detection experiments on these two types of sensors. The results demonstrated that the limit of detection (LOD) of CA125 on the AuAg-SPR sensor was 0.1 U/mL (0.8 ng/mL) based on its direct reaction with an immobilised antibody, which was two orders of magnitude lower than that of the Au-SPR sensor (10 U/mL). The total changes in the resonance wavelength (∆λ_R) of the former were 1.7-fold those of the latter. The volume fractions of the adsorbates (f_ad) and effective RIs (n_adlayer) in each adlayer were then calculated and the effect of the antibody size on the detection results was analysed. The AuAg-SPR sensors had a higher sensitivity than the conventional Au-SPR sensors for detecting CA125 due to their electric field characteristics. Therefore, these will have better application prospects.

A portable electrochemical immunosensor for highly sensitive point-of-care testing of genetically modified crops

The wide cultivation of genetically modified (GM) crops has raised concerns on the risks to humans and the environment. 5-enolpyruvylshikimate-3-phosphate synthase isolated from Agrobacterium species strain CP4 (CP4-EPSPS) protein is most widely present in these crops. Therefore the measurement of CP4-EPSPS sensitively in a point-of-care testing (POCT) manner for the screening of transgenic plants is demanded. To date the development of quantitative POCT system has not yet been reported. In presented study, an electrochemical immunosensor towards CP4-EPSPS has been fabricated by integrating a portable bioanalytical device with a disposable screen-printed carbon electrode (SPCE) for POCT of GM crops. The dual-functionalized AuNPs were used as nanoprobes and prepared by simultaneously tagging horseradish peroxidase (HRP) and antibody on AuNPs with an exceptionally simple protocol. The sensitivity of the developed nanoprobe-based immunosensor was 62.5-fold higher than that using HRP-labeled antibody. As a result, the proposed immunosensor using SPCE could detect CP4-EPSPS down to 0.050 ng mL^-1 with the linear range of 0.10-10 ng mL^-1 within 65 min. In addition, the developed method has been validated with genuine GM crops and the results show a good correlation coefficient of 0.9909 compared with those of a commercial ELISA kit. Therefore, this portable electrochemical immunosensor is suitable for rapid and sensitive detection and provides a convenient and reliable platform for POCT assay.

Temperature-regulated protein adsorption on a PNIPAm layer

In immunosensors, antibody orientation is a key factor that determines the sensitivity of a device. To date much effort has been devoted to exploring strategies for the direct control of the orientation of antibodies immobilized on a bioactive surface, but less attention has been paid to controlling the orientation of intermediate proteins (though usually used when immobilizing antibodies), which may greatly limit the sensitivity of immunological activities. Therefore, it is of great significance to seek novel methods for controlling protein orientation. Here, we design a new strategy for controlling protein orientation. The main idea is to bind proteins to a ligand-functionalized poly(N-isopropylacrylamide) (PNIPAm) layer, and then the protein orientation can be mediated by environmental temperature. The theory predicts that the protein orientation can show unexpected triple-thermo-responsive behavior. Based on the fraction of ligand adsorbed by the protein, the reponsive behavior can be either complete adsorption or partial adsorption, which is determind by the polymer's surface coverage and the protein's properties. We expect that the present strategy can enrich the methods for controlling intermediate protein orientation and can guide the design of novel immunosensors with superior sensitivity.

Ultrasensitive interdigitated capacitance immunosensor using gold nanoparticles

Immunosensors based on interdigitated electrodes (IDEs), have recently demonstrated significant improvements in the sensitivity of capacitance detection. Herein, a novel type of highly sensitive, compact and portable immunosensor based on a gold interdigital capacitor has been designed and developed for the rapid detection of hepatitis B surface antigen (HBsAg). To improve the efficiency of antibody immobilization and time-saving, a self-assembled monolayer (SAM) of 2-mercaptoethylamine film was coated on IDEs. Afterwards, carboxyl groups on primary antibodies were activated through 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide and were immobilized on amino-terminated SAM for better control of the oriented immobilization of antibodies on gold IDEs. In addition, gold nanoparticles conjugated with a secondary antibody were used to enhance the sensitivity. Under optimal conditions, the immunosensor exhibited the sensitivity of 0.22 nF.pg ml^-1, the linear range from 5 pg ml^-1 to 1 ng ml^-1 and the detection limit of 1.34 pg ml^-1, at a signal-to-noise ratio of 3.

Sensitive and Facile Electrochemiluminescent Immunoassay for Detecting Genetically Modified Rapeseed Based on Novel Carbon Nanoparticles

A highly sensitive electrochemiluminescent (ECL) immunoassay targeting PAT/ bar protein was facilely developed for genetically modified (GM) rapeseed detection using carbon nanoparticles (CNPs) originally prepared from printer toner. In this work, CNPs linked with antibody for PAT/ bar protein were used to modify a working electrode. After an immunoreaction between the PAT/ bar protein and its antibody, the immunocomplex formed on the electrode receptor region resulted in an inhibition of electron transfer between the electrode surface and the ECL substance, thus led to a decrease of ECL response. Under the optimal conditions, the ECL responses linearly decreased as the increase of the PAT/ bar protein concentration and the GM rapeseed RF3 content in the ranges of 0.10-10 ng/mL and 0.050-1.0%, with the limits of detection of 0.050 ng/mL and 0.020% (S/N = 3). These results open a facile, sensitive, and rapid approach for the safety control of agricultural GM rape.

The synthesis of a smart streptavidin-functionalized poly(N-isopropylacrylamide) composite and its application in the separation and detection of virus nucleic acid

A new kind of polymeric material (PNIPAAm-co-SA) was prepared by conjugating a thermosensitive polymer, Poly (N-isopropylacrylamide) (PNIPAAm) with streptavidin (SA). This smart prepared composite displayed a controllable conformation change between an expanded and a collapsed form, below or above its lower critical solution temperature (LCST). Differential scanning calorimetry (DSC) analysis demonstrated that the PNIPAAm-co-SA bioconjugate showed the same LCST as the original synthetic polymer, PNIPAAm, which was also 32°C. Based on the specific interaction between SA and biotin, a higher capture efficiency of PNIPAAm-co-SA, which was almost 100% in PBS buffer solution and above 70% in serum was obtained, respectively. And the high affinity between PNIPAAm-co-SA and biotin was still maintained after three heating cycles. Subsequently, the variola virus (small pox, VV) oligonucleotide sequence was chosen as a model to demonstrate the sensitivity of the biosensor which was fabricated based on PNIPAAm-co-SA. The biosensor exhibited the ability to separate and enrich targets from complicated system with its phase transition ability, and high sensitivity toward VV-targets were achieved. Moreover, other types of targets such as proteins and cells, could be detected by changing the biotin-captures, which indicated the broad applicability of biosensors based on this smart polymer material.

Nanomaterial-based biosensors for detection of prostate specific antigen

Screening serum for the presence of prostate specific antigen (PSA) belongs to the most common approach for the detection of prostate cancer. This review (with 156 refs.) addresses recent developments in PSA detection based on the use of various kinds of nanomaterials. It starts with an introduction into the field, the significance of testing for PSA, and on current limitations. A first main section treats electrochemical biosensors for PSA, with subsections on methods based on the use of gold electrodes, graphene or graphene-oxide, carbon nanotubes, hybrid nanoparticles, and other types of nanoparticles. It also covers electrochemical methods based on the enzyme-like activity of PSA, on DNA-, aptamer- and biofuel cell-based methods, and on the detection of PSA via its glycan part. The next main section covers optical biosensors, with subsections on methods making use of surface plasmon resonance (SPR), localized SPR and plasmonic ELISA-like schemes. This is followed by subsections on methods based on the use of fiber optics, fluorescence, chemiluminescence, Raman scattering and SERS, electrochemiluminescence and cantilever-based methods. The most sensitive biosensors are the electrochemical ones, with lowest limits of detection (down to attomolar concentrations), followed by mass cantilever sensing and electrochemilumenescent strategies. Optical biosensors show lower performance, but are still more sensitive compared to standard ELISA. The most commonly applied nanomaterials are metal and carbon-based ones and their hybrid composites used for different amplification strategies. The most attractive sensing schemes are summarized in a Table. The review ends with a section on conclusions and perspectives.

Recent Advances in Electrochemical Immunosensors

Immunosensors have experienced a very significant growth in recent years, driven by the need for fast, sensitive, portable and easy-to-use devices to detect biomarkers for clinical diagnosis or to monitor organic pollutants in natural or industrial environments. Advances in the field of signal amplification using enzymatic reactions, nanomaterials such as carbon nanotubes, graphene and graphene derivatives, metallic nanoparticles (gold, silver, various oxides or metal complexes), or magnetic beads show how it is possible to improve collection, binding or transduction performances and reach the requirements for realistic clinical diagnostic or environmental control. This review presents these most recent advances; it focuses first on classical electrode substrates, then moves to carbon-based nanostructured ones including carbon nanotubes, graphene and other carbon materials, metal or metal-oxide nanoparticles, magnetic nanoparticles, dendrimers and, to finish, explore the use of ionic liquids. Analytical performances are systematically covered and compared, depending on the detection principle, but also from a chronological perspective, from 2012 to 2016 and early 2017.

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.