Cancer Biomarker Detection in Serum Samples Using Surface Plasmon Resonance and Quartz Crystal Microbalance Sensors with Nanoparticle Signal Amplification

Biosensors for Public Health and Environmental Monitoring: The Case for Sustainable Biosensing

Climate change is a profound crisis that affects every aspect of life, including public health. Changes in environmental conditions can promote the spread of pathogens and the development of new mutants and strains. Early detection is essential in managing and controlling this spread and improving overall health outcomes. This perspective article introduces basic biosensing concepts and various biosensors, including electrochemical, optical, mass-based, nano biosensors, and single-molecule biosensors, as important sustainability and public health preventive tools. The discussion also includes how the sustainability of a biosensor is crucial to minimizing environmental impacts and ensuring the long-term availability of vital technologies and resources for healthcare, environmental monitoring, and beyond. One promising avenue for pathogen screening could be the electrical detection of biomolecules at the single-molecule level, and some recent developments based on single-molecule bioelectronics using the Scanning Tunneling Microscopy-assisted break junctions (STM-BJ) technique are shown here. Using this technique, biomolecules can be detected with high sensitivity, eliminating the need for amplification and cell culture steps, thereby enhancing speed and efficiency. Furthermore, the STM-BJ technique demonstrates exceptional specificity, accurately detects single-base mismatches, and exhibits a detection limit essentially at the level of individual biomolecules. Finally, a case is made here for sustainable biosensors, how they can help, the paradigm shift needed to achieve them, and some potential applications.

Biosensors for metastatic cancer cell detection

Early detection and effective cancer treatment are critical to improving metastatic cancer cell diagnosis and management today. In particular, accurate qualitative diagnosis of metastatic cancer cell represents an important step in the diagnosis of cancer. Today, biosensors have been widely developed due to the daily need to measure different chemical and biological species. Biosensors are utilized to quantify chemical and biological phenomena by generating signals that are directly proportional to the quantity of the analyte present in the reaction. Biosensors are widely used in disease control, drug delivery, infection detection, detection of pathogenic microorganisms, and markers that indicate a specific disease in the body. These devices have been especially popular in the field of metastatic cancer cell diagnosis and treatment due to their portability, high sensitivity, high specificity, ease of use and short response time. This article examines biosensors for metastatic cancer cells. It also studies metastatic cancer cells and the mechanism of metastasis. Finally, the function of biosensors and biomarkers in metastatic cancer cells is investigated.

Controlling Adsorption of Diblock Copolymer Nanoparticles onto an Aldehyde-Functionalized Hydrophilic Polymer Brush via pH Modulation

Sterically stabilized diblock copolymer nanoparticles with a well-defined spherical morphology and tunable diameter were prepared by RAFT aqueous emulsion polymerization of benzyl methacrylate at 70 °C. The steric stabilizer precursor used for these syntheses contained pendent cis-diol groups, which means that such nanoparticles can react with a suitable aldehyde-functional surface via acetal bond formation. This principle is examined herein by growing an aldehyde-functionalized polymer brush from a planar silicon wafer and studying the extent of nanoparticle adsorption onto this model substrate from aqueous solution at 25 °C using a quartz crystal microbalance (QCM). The adsorbed amount, Γ, depends on both the nanoparticle diameter and the solution pH, with minimal adsorption observed at pH 7 or 10 and substantial adsorption achieved at pH 4. Variable-temperature QCM studies provide strong evidence for chemical adsorption, while scanning electron microscopy images recorded for the nanoparticle-coated brush surface after drying indicate mean surface coverages of up to 62%. This fundamental study extends our understanding of the chemical adsorption of nanoparticles on soft substrates.

Application of biosensors in cancers, an overview

The deadliest disease in the world, cancer, kills many people every year. The early detection is the only hope for the survival of malignant cancer patients. As a result, in the preliminary stages of, the diagnosis of cancer biomarkers at the cellular level is critical for improving cancer patient survival rates. For decades, scientists have focused their efforts on the invention of biosensors. Biosensors, in addition to being employed in other practical scenarios, can essentially function as cost effective and highly efficient devices for this purpose. Traditional cancer screening procedures are expensive, time-consuming, and inconvenient for repeat screenings. Biomarker-based cancer diagnosis, on the other hand, is rising as one of the most potential tools for early detection, disease progression monitoring, and eventual cancer treatment. As Biosensor is an analytical device, it allows the selected analyte to bind to the biomolecules being studied (for example RNA, DNA, tissue, proteins, and cells). They can be divided based on the kind of biorecognition or transducer elements on the sensor. Most biosensor analyses necessitate the analyte being labeled with a specific marker. In this review article, the application of distinct variants of biosensors against cancer has been described.

Strategies for Mitigating Commercial Sensor Chip Variability with Experimental Design Controls

Surface plasmon resonance (SPR) is a popular real-time technique for the measurement of binding affinity and kinetics, and bench-top instruments combine affordability and ease of use with other benefits of the technique. Biomolecular ligands labeled with the 6xHis tag can be immobilized onto sensing surfaces presenting the Ni2+-nitrilotriacetic acid (NTA) functional group. While Ni-NTA immobilization offers many advantages, including the ability to regenerate and reuse the sensors, its use can lead to signal variability between experimental replicates. We report here a study of factors contributing to this variability using the Nicoya OpenSPR as a model system and suggest ways to control for those factors, increasing the reproducibility and rigor of the data. Our model ligand/analyte pairs were two ovarian cancer biomarker proteins (MUC16 and HE4) and their corresponding monoclonal antibodies. We observed a broad range of non-specific binding across multiple NTA chips. Experiments run on the same chips had more consistent results in ligand immobilization and analyte binding than experiments run on different chips. Further assessment showed that different chips demonstrated different maximum immobilizations for the same concentration of injected protein. We also show a variety of relationships between ligand immobilization level and analyte response, which we attribute to steric crowding at high ligand concentrations. Using this calibration to inform experimental design, researchers can choose protein concentrations for immobilization corresponding to the linear range of analyte response. We are the first to demonstrate calibration and normalization as a strategy to increase reproducibility and data quality of these chips. Our study assesses a variety of factors affecting chip variability, addressing a gap in knowledge about commercially available sensor chips. Controlling for these factors in the process of experimental design will minimize variability in analyte signal when using these important sensing platforms.

Recognizing the Less Explored "Active Solid"-"Moving Liquid" Interfaces in Bio/Chemical Sensors

Bio/chemical sensors possess a plethora of advantageous features that have proven to be invaluable tools in detecting and monitoring biomolecules, facilitating advancements in healthcare, environmental monitoring, food safety, and more. However, when it comes to their routine use in continuous fluid flow conditions, an intricate web of solid-liquid interfacial phenomena emerges, which requires a deep understanding of the sensor surface and fluid interations. These interfacial phenomena encompass a broad spectrum of physical, chemical, and biological processes, other than the actual detection, that influence the sensor's response. In this context, perhaps exploring a new theme "active solid"-"moving liquid" interface will unleash the full potential of bio/chemical sensors in any flow-based application.

Application of the Nicoya OpenSPR to Studies of Biomolecular Binding: A Review of the Literature from 2016 to 2022

The Nicoya OpenSPR is a benchtop surface plasmon resonance (SPR) instrument. As with other optical biosensor instruments, it is suitable for the label-free interaction analysis of a diverse set of biomolecules, including proteins, peptides, antibodies, nucleic acids, lipids, viruses, and hormones/cytokines. Supported assays include affinity/kinetics characterization, concentration analysis, yes/no assessment of binding, competition studies, and epitope mapping. OpenSPR exploits localized SPR detection in a benchtop platform and can be connected with an autosampler (XT) to perform automated analysis over an extended time period. In this review article, we provide a comprehensive survey of the 200 peer-reviewed papers published between 2016 and 2022 that use the OpenSPR platform. We highlight the range of biomolecular analytes and interactions that have been investigated using the platform, provide an overview on the most common applications for the instrument, and point out some representative research that highlights the flexibility and utility of the instrument.

Antibody Immobilization on Sulfated Cellulose Nanocrystals

Exploiting cellulose nanocrystals' high aspect ratio and tailorable surface for immunological biosensors has been hindered by the relatively limited research on using commonly available sulfated cellulose nanocrystals (CNCs) for antibody immobilization and by the low hydrolytic stability of dried assemblies produced from sulfated CNCs. Herein, we report a reaction scheme that enables both hydrolytic stability and antibody immobilization through 3-aminopropyl-triethoxysilane and glutaric anhydride chemistry. Immobilization was demonstrated using three model antibodies used in the detection of the cancer biomarkers: alpha-fetoprotein, prostate-specific antigen, and carcinoembryonic antigen. Thermogravimetric analysis coupled with Fourier-transform infrared spectroscopy provided evidence of CNC modification. Quartz crystal microbalance with dissipation monitoring was used to monitor binding during each step of the immobilization scheme as well as binding of the corresponding antigens. The general reaction scheme was tested using both aqueous CNC dispersions and CNC films. Film modification is slightly simpler as it avoids centrifugation and washing steps. However, modifying the dispersed CNCs provides access to their entire surface area and results in a greater capacity for antigen binding.

Development of Electrochemical Immunosensors for HER-1 and HER-2 Analysis in Serum for Breast Cancer Patients

In this work, two human epidermal growth factor receptors, HER-1 and HER-2, were selected as biomarkers to enable the detection of breast cancer. Therefore, two biosensors were developed using gold sensor chips coupled with amperometric detection of the enzyme label horse radish peroxidase (HRP). The biosensors/immunosensors relied on indirect sandwich enzyme-linked immunosorbent assays with monoclonal antibodies (Ab) against HER-1 and HER-2 attached to the sensors to capture the biomarkers. Detection polyclonal antibodies followed by secondary anti-rabbit (for HER-1) and anti-goat (for HER-2) IgG antibody-HRP were then applied for signal generation. In buffer, the developed sensors showed limits of detections (LOD) of 1.06 ng mL^-1 and 0.95 ng mL^-1 and limits of quantification (LOQ) of 2.1 ng mL^-1 and 1.5 ng mL^-1 for HER-1 and HER-2, respectively. In 100% (undiluted) serum, LODs of 1.2 ng mL^-1 and 1.47 ng mL^-1 and LOQs of 1.5 ng mL^-1 and 2.1 ng mL^-1 were obtained for HER-1 and HER-2, respectively. Such limits of detections are within the serum clinical range for the two biomarkers. Furthermore, gold nanoparticles (AuNP) labelled with secondary anti-rabbit and anti-goat IgG antibody-HRP were then used to enhance the assay signal and increase the sensitivity. In buffers, LODs of 30 pg mL^-1 were seen for both sensors and LOQs of 98 pg mL^-1 and 35 pg mL^-1 were recorded for HER-1 and HER-2, respectively. For HER-2 the AuNPs biosensor was also tested in 100% serum obtaining a LOD of 50 pg mL^-1 and a LOQ of 80 pg mL^-1. The HER-2 AuNP electrochemical immunosensor showed high specificity with very low cross-reactivity to HER-1. These findings demonstrate that the two developed sensors can enable early detection as well as monitoring of disease progression with a beneficial impact on patient survival and clinical outcomes.

An immunogold single extracellular vesicular RNA and protein (Au SERP) biochip to predict responses to immunotherapy in non-small cell lung cancer patients

Conventional PD-L1 immunohistochemical tissue biopsies only predict 20%-40% of non-small cell lung cancer (NSCLC) patients that will respond positively to anti-PD-1/PD-L1 immunotherapy. Herein, we present an immunogold biochip to quantify single extracellular vesicular RNA and protein (Au SERP) as a non-invasive alternative. With only 20 μl of purified serum, PD-1/PD-L1 proteins on the surface of extracellular vesicles (EVs) and EV PD-1/PD-L1 messenger RNA (mRNA) cargo were detected at a single-vesicle resolution and exceeded the sensitivities of their bulk-analysis conventional counterparts, ELISA and qRT-PCR, by 1000 times. By testing a cohort of 27 non-responding and 27 responding NSCLC patients, Au SERP indicated that the single-EV mRNA biomarkers surpass the single-EV protein biomarkers in predicting patient responses to immunotherapy. Dual single-EV PD-1/PD-L1 mRNA detection differentiated responders from non-responders with an accuracy of 72.2% and achieved an NSCLC diagnosis accuracy of 93.2%, suggesting the potential for Au SERP to provide enhanced immunotherapy predictions and cancer diagnoses within the clinical setting.

Autofluorescence Imaging of Living Yeast Cells with Deep-Ultraviolet Surface Plasmon Resonance

Autofluorescence in living cells on aluminum thin film was excited with deep-ultraviolet surface plasmon resonance (deep-UV SPR). Deep-UV SPR under aqueous medium was excited with Kretschmann configuration by using a sapphire prism. Deep-UV SPR is one of the promising techniques for high-sensitive autofluorescence imaging of living cells without staining. Label-free observation is significant for the structural analysis of living cells. We demonstrated the high-sensitive autofluorescence imaging of living yeast cells with deep-UV SPR. We applied a high refractive index prism, such as sapphire, which is suitable for the observation of specimens in aqueous medium, to excite deep-UV SPR. Although typical autofluorescence from living cells is buried in background noise, deep-UV SPR enhances the autofluorescence signal. The deep-UV SPR excitation of an aluminum thin film through a sapphire prism was investigated theoretically and experimentally. It showed that the fluorescence intensities are increased 2.8-fold. Deep-UV SPR enhanced the autofluorescence of cell structures, and yeast cells were found to be very sensitive. As a result, for water-immersed specimens, the sapphire-prism-based Kretschmann configuration excited SPR in deep-UV. Findings from this study suggest that deep-UV SPR can be considered an effective technique for attaining high-sensitivity observation of biological samples.

An ultrasensitive biosensor for prostate specific antigen detection in complex serum based on functional signal amplifier and designed peptides with both antifouling and recognizing capabilities

The development of biosensors capable of averting biofouling and detecting biomarkers in complex biological media remains a challenge. Herein, an ultralow fouling and highly sensitive biosensor based on specifically designed antifouling peptides and a signal amplification strategy was designed for prostate specific antigen (PSA) detection in human serum. A low fouling layer of poly(ethylene glycol) (PEG) doped the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) was electrodeposited on the electrode surface, followed by the immobilization of streptavidin and further attachment of biotin-labelled peptides. The peptide was designed to include PSA specific recognition domain (HSSKLQK) and antifouling domain (PPPPEKEKEKE), and the terminal of the peptide was functionalized with -SH group. DNA functionalized gold nanorods (DNA/AuNRs) were then attached to the electrode, and methylene blue (MB) molecules were adsorbed to the DNA to form the signal amplifier. In the presence of PSA, the peptide was specifically cleaved and resulted in the loss of AuNRs together with DNA and MB, and thus significant decrease of the current signal. The biosensor exhibited a low limit of detection (LOD) of 0.035 pg mL^-1 (S/N = 3), with a wide linear range from 0.10 pg mL^-1 to 10.0 ng mL^-1, and it was able to detect PSA in real human serum owing to the presence of the antifouling peptides, indicating great potential of the constructed biosensor for practical application.

Dual-Mode and Label-Free Detection of Exosomes from Plasma Using an Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring

The biomolecular contents of extracellular vesicles, such as exosomes, have been shown to be crucial in intercellular communication and disease propagation. As a result, there has been a recent surge in the exploration of novel biosensing platforms that can sensitively and specifically detect exosomal content such as proteins and nucleic acids, with a view toward application in diagnostic assays. Here, we demonstrate dual-mode and label-free detection of plasma exosomes using an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The platform adopts a direct immunosensing approach to effectively capture exosomes via their surface protein expression of CD63. By combining QCM-D with a tandem in situ electrochemical impedance spectroscopy measurement, we are able to demonstrate relationships between mass, viscoelasticity and impedance inducing properties of each functional layer and analyte. In addition to lowering the limit of detection (by a factor of 2-4) to 6.71 × 10⁷ exosome-sized particles (ESP) per mL in 25% v/v serum, the synergy between dissipation and impedance response introduces improved sensing specificity by offering further distinction between soft and rigid analytes, thereby promoting EQCM-D as an important technique for exosome analysis.

Distinctive Adsorption Mechanism and Kinetics of Immunoglobulin G on a Nanoscale Polymer Surface

Elucidation of protein adsorption beyond simple polymer surfaces to those presenting greater chemical complexity and nanoscopic features is critical to developing well-controlled nanobiomaterials and nanobiosensors. In this study, we repeatedly and faithfully track individual proteins on the same nanodomain areas of a block copolymer (BCP) surface and monitor the adsorption and assembly behavior of a model protein, immunoglobulin G (IgG), over time into a tight surface-packed structure. With discrete protein adsorption events unambiguously visualized at the biomolecular level, the detailed assembly and packing states of IgG on the BCP nanodomain surface are subsequently correlated to various regimes of IgG adsorption kinetic plots. Intriguing features, entirely different from those observed from macroscopic homopolymer templates, are identified from the IgG adsorption isotherms on the nanoscale, chemically varying BCP surface. They include the presence of two Langmuir-like adsorption segments and a nonmonotonic regime in the adsorption plot. Via correlation to time-corresponding topographic data, the unique isotherm features are explained with single biomolecule level details of the IgG adsorption pathway on the BCP. This work not only provides much needed, direct experimental evidence for time-resolved, single protein level, adsorption events on nanoscale polymer surfaces but also signifies mutual linking between specific topographic states of protein adsorption and assembly to particular segments of adsorption isotherms. From the fundamental research viewpoint, the correlative ability to examine the nanoscopic surface organizations of individual proteins and their local as well as global adsorption kinetic profiles will be highly valuable for accurately determining protein assembly mechanisms and interpreting protein adsorption kinetics on nanoscale surfaces. Application-wise, such knowledge will also be important for fundamentally guiding the design and development of biomaterials and biomedical devices that exploit nanoscale polymer architectures.

Highly portable quantitative screening test for prostate-specific antigen at point of care

Prostate cancer (PCa) is the second most diagnosed cancer among men. Targeted PCa screening may decrease PCa-specific mortality. Prostate-specific antigen (PSA) is the most reliable and widely accepted tumor biomarker for screening and monitoring PCa status. However, in many settings, quantification of serum PSA requires access to centralized laboratories. In this study, we describe a proof-of-concept rapid test combined with a highly portable Cube^™ reader for quantification of total PSA from a drop of serum within 20 min. We demonstrated the application of gold nanoshells as a label for lateral flow assay with significant increase in the measured colorimetric signal intensity to achieve five times lower detection limit when compared to the traditionally used 40 nm gold nanosphere labels, without a need for any additional signal amplification steps. We first optimized and evaluated the performance of the assay with commercially available total PSA calibrators. For initial validation with commercially available ACCESS Hybritech PSA calibrator, a detection range of 0.5-150 ng/mL was achieved. We compared the performance of our total PSA test with IMMULITE analyzer for quantification of total PSA in archived human serum samples. On preliminary testing with archived serums samples and comparison with IMMULITE total PSA assay, a correlation of 0.95 (p < .0001) was observed. The highly portable quantitative screening test for PSA described in this study has the potential to make PCa screening more accessible where diagnostic labs and automated immunoassay systems are not available, to reduce therapeutic turnaround time, to streamline clinical care, and to direct patient care for both initial screening and for post-treatment monitoring of patients.

Dual-Mode and Label-Free Detection of Exosomes from Plasma Using an Electrochemical Quartz Crystal Microbalance with Dissipation Monitoring

The biomolecular contents of extracellular vesicles, such as exosomes, have been shown to be crucial in intercellular communication and disease propagation. As a result, there has been a recent surge in the exploration of novel biosensing platforms that can sensitively and specifically detect exosomal content such as proteins and nucleic acids, with a view toward application in diagnostic assays. Here, we demonstrate dual-mode and label-free detection of plasma exosomes using an electrochemical quartz crystal microbalance with dissipation monitoring (EQCM-D). The platform adopts a direct immunosensing approach to effectively capture exosomes via their surface protein expression of CD63. By combining QCM-D with a tandem in situ electrochemical impedance spectroscopy measurement, we are able to demonstrate relationships between mass, viscoelasticity and impedance inducing properties of each functional layer and analyte. In addition to lowering the limit of detection (by a factor of 2–4) to 6.71 × 10⁷ exosome-sized particles (ESP) per mL in 25% v/v serum, the synergy between dissipation and impedance response introduces improved sensing specificity by offering further distinction between soft and rigid analytes, thereby promoting EQCM-D as an important technique for exosome analysis.

AC-Electroosmosis-Assisted Surface Plasmon Resonance Sensing for Enhancing Protein Signals with a Simple Kretschmann Configuration

A surface plasmon resonance (SPR) sensor chip fabricated with a comb-shaped microelectrode array to supply alternating current (AC) voltage is reported. The chip induces circulating flow near the surface (i.e., AC electroosmosis). The circulating flow provides a mixing effect, which enhances the binding of the analyte molecules. We evaluated the SPR characteristics of the chip and demonstrated an improvement in protein binding to the chip surface. SPR sensor chips with comb-shaped microelectrodes were fabricated using standard UV lithography. Sensing experiments were conducted using a standard Kretschmann-type SPR measurement system. To demonstrate the mixing effect of AC electroosmosis, we evaluated the binding of immunoglobulin G molecules onto the sensor surface where anti-immunoglobulin G antibodies were covalently immobilized. The result indicates that the amount of binding increases by a factor of 1.7 above that achieved by using a conventional chip, suggesting enhancement of the protein signal.

Acoustic Biosensors and Microfluidic Devices in the Decennium: Principles and Applications

Lab-on-a-chip (LOC) technology has gained primary attention in the past decade, where label-free biosensors and microfluidic actuation platforms are integrated to realize such LOC devices. Among the multitude of technologies that enables the successful integration of these two features, the piezoelectric acoustic wave method is best suited for handling biological samples due to biocompatibility, label-free and non-invasive properties. In this review paper, we present a study on the use of acoustic waves generated by piezoelectric materials in the area of label-free biosensors and microfluidic actuation towards the realization of LOC and POC devices. The categorization of acoustic wave technology into the bulk acoustic wave and surface acoustic wave has been considered with the inclusion of biological sample sensing and manipulation applications. This paper presents an approach with a comprehensive study on the fundamental operating principles of acoustic waves in biosensing and microfluidic actuation, acoustic wave modes suitable for sensing and actuation, piezoelectric materials used for acoustic wave generation, fabrication methods, and challenges in the use of acoustic wave modes in biosensing. Recent developments in the past decade, in various sensing potentialities of acoustic waves in a myriad of applications, including sensing of proteins, disease biomarkers, DNA, pathogenic microorganisms, acoustofluidic manipulation, and the sorting of biological samples such as cells, have been given primary focus. An insight into the future perspectives of real-time, label-free, and portable LOC devices utilizing acoustic waves is also presented. The developments in the field of thin-film piezoelectric materials, with the possibility of integrating sensing and actuation on a single platform utilizing the reversible property of smart piezoelectric materials, provide a step forward in the realization of monolithic integrated LOC and POC devices. Finally, the present paper highlights the key benefits and challenges in terms of commercialization, in the field of acoustic wave-based biosensors and actuation platforms.

A Comparison of EIS and QCM NanoMIP-Based Sensors for Morphine

In this work we have compared two different sensing platforms for the detection of morphine as an example of a low molecular weight target analyte. For this, molecularly imprinted polymer nanoparticles (NanoMIP), synthesized with an affinity towards morphine, were attached to an electrochemical impedance spectroscopy (EIS) and a quartz crystal microbalance (QCM) sensor. Assay design, sensors fabrication, analyte sensitivity and specificity were performed using similar methods. The results showed that the EIS sensor achieved a limit of detection (LOD) of 0.11 ng·mL-1, which is three orders of magnitude lower than the 0.19 µg·mL-1 achieved using the QCM sensor. Both the EIS and the QCM sensors were found to be able to specifically detect morphine in a direct assay format. However, the QCM method required conjugation of gold nanoparticles (AuNPs) to the small analyte (morphine) to amplify the signal and achieve a LOD in the µg·mL-1 range. Conversely, the EIS sensor method was labor-intensive and required extensive data handling and processing, resulting in longer analysis times (~30-40 min). In addition, whereas the QCM enables visualization of the binding events between the target molecule and the sensor in real-time, the EIS method does not allow such a feature and measurements are taken post-binding. The work also highlighted the advantages of using QCM as an automated, rapid and multiplex sensor compared to the much simpler EIS platform used in this work, though, the QCM method will require sample preparation, especially when a sensitive (ng·mL-1) detection of a small analyte is needed.

Biosensing strategies for diagnosis of prostate specific antigen

Almost from the time of its discovery, the prostate specific antigen (PSA) has been one of the most accurate and most extensively studied indicators of prostate cancer (PC). Because of advancements in biosensing systems and technology, PSA analysis methods have been substantially updated and enhanced as compared to their first instances. With the development of techniques in biosensor technology, the number of PSA biosensors that can be used in the biomedical sector is increasing year by year. Many different recognition elements and transducers have been used in the development of biosensor systems that exhibit high sensitivity, selectivity, and specificity. Here in this review, we provide a current overview of the different approaches to PSA detection.

A Fabry-Pérot cavity coupled surface plasmon photodiode for electrical biomolecular sensing

Surface plasmon resonance is a well-established technology for real-time highly sensitive label-free detection and measurement of binding kinetics between biological samples. A common drawback, however, of surface plasmon resonance detection is the necessity for far field angular resolved measurement of specular reflection, which increases the size as well as requiring precise calibration of the optical apparatus. Here we present an alternative optoelectronic approach in which the plasmonic sensor is integrated within a photovoltaic cell. Incident light generates an electronic signal that is sensitive to the refractive index of a solution via interaction with the plasmon. The photogenerated current is enhanced due to the coupling of the plasmon mode with Fabry-Pérot modes in the absorbing layer of the photovoltaic cell. The near field electrical detection of surface plasmon resonance we demonstrate will enable a next generation of cheap, compact and high throughput biosensors.

Surface plasmon resonance is well established for biosensing applications, but commonly limited by complex optical detection. Here, the authors present a plasmonic sensor integrated in a photovoltaic cell, which generates an electronic signal sensitive to the solution refractive index via plasmon interaction

Recent Advancements in Receptor Layer Engineering for Applications in SPR-Based Immunodiagnostics

The rapid progress in the development of surface plasmon resonance-based immunosensing platforms offers wide application possibilities in medical diagnostics as a label-free alternative to enzyme immunoassays. The early diagnosis of diseases or metabolic changes through the detection of biomarkers in body fluids requires methods characterized by a very good sensitivity and selectivity. In the case of the SPR technique, as well as other surface-sensitive detection strategies, the quality of the transducer-immunoreceptor interphase is crucial for maintaining the analytical reliability of an assay. In this work, an overview of general approaches to the design of functional SPR-immunoassays is presented. It covers both immunosensors, the design of which utilizes well-known and often commercially available substrates, as well as the latest solutions developed in-house. Various approaches employing chemical and passive binding, affinity-based antibody immobilization, and the introduction of nanomaterial-based surfaces are discussed. The essence of their influence on the improvement of the main analytical parameters of a given immunosensor is explained. Particular attention is paid to solutions compatible with the latest trends in the development of label-free immunosensors, such as platforms dedicated to real-time monitoring in a quasi-continuous mode, the use of in situ-generated receptor layers (elimination of the regeneration step), and biosensors using recombinant and labelled protein receptors.

Electrochemistry-Assisted Surface Plasmon Resonance Biosensor for Detection of CA 15-3

In this work, we describe an innovative methodology based on combined surface plasmon resonance (SPR) and electrochemical responses (eSPR) in the same immunoassay for screening CA 15-3 cancer biomarker with high sensitivity (and selectivity), in a very simple, label-free, accurate, and fully automated manner. Detection was achieved by performing two simple steps. In the first step, direct SPR was used to monitor CA 15-3 interaction with surface immobilized antibody. Two linear response ranges were obtained and the detection limit achieved is poor (LOD of 21 U mL^-1). However, in the second detection step, electrochemical measurements at the SPR gold surface were performed to measure the decrease of redox probe peak current upon antigen-antibody interaction, providing a suitable amplification strategy to lower detection levels of CA 15-3 (LOD of 0.0998 U mL^-1), without the need of additional complex and/or expensive amplification steps to enhance the sensitivity. Moreover, selectivity studies were performed against other common cancer biomarkers and the results showed that the eSPR immunosensor is selective for the CA 15-3 protein. Finally, the clinical applicability of the developed eSPR biosensing methodology was successfully applied to detect CA 15-3 in human serum samples at clinically relevant levels due to the high sensitivity of electrochemical readout. The same concept may be further extended to other proteins of interest.

Graphene FET Sensors for Alzheimer's Disease Protein Biomarker Clusterin Detection

We report on the fabrication and characterisation of graphene field-effect transistor (GFET) biosensors for the detection of Clusterin, a prominent protein biomarker of Alzheimer’s disease (AD). The GFET sensors were fabricated on Si/SiO₂ substrate using photolithographic patterning and metal lift-off techniques with evaporated chromium and sputtered gold contacts. Raman Spectroscopy was performed on the devices to determine the quality of the graphene. The GFETs were annealed to improve their performance before the channels were functionalized by immobilising the graphene surface with linker molecules and anti-Clusterin antibodies. Concentration of linker molecules was also independently verified by absorption spectroscopy using the highly collimated micro-beam light of Diamond B23 beamline. The detection was achieved through the binding reaction between the antibody and varying concentrations of Clusterin antigen from 1 to 100 pg/mL, as well as specificity tests using human chorionic gonadotropin (hCG), a glycoprotein risk biomarker of certain cancers. The GFETs were characterized using direct current (DC) 4-probe electrical resistance (4-PER) measurements, which demonstrated a limit of detection of the biosensors to be ∼ 300 fg/mL (4 fM). Comparison with back-gated Dirac voltage shifts with varying concentration of Clusterin show 4-PER measurements to be more accurate, at present, and point to a requirement for further optimisation of the fabrication processes for our next generation of GFET sensors. Thus, we have successfully fabricated a promising set of GFET biosensors for the detection of Clusterin protein biomarker. The developed GFET biosensors are entirely generic and also have the potential to be applied to a variety of other disease detection applications such as Parkinson’s, cancer, and cardiovascular.

Nanostructures for Biosensing, with a Brief Overview on Cancer Detection, IoT, and the Role of Machine Learning in Smart Biosensors

Biosensors are essential tools which have been traditionally used to monitor environmental pollution and detect the presence of toxic elements and biohazardous bacteria or virus in organic matter and biomolecules for clinical diagnostics. In the last couple of decades, the scientific community has witnessed their widespread application in the fields of military, health care, industrial process control, environmental monitoring, food-quality control, and microbiology. Biosensor technology has greatly evolved from in vitro studies based on the biosensing ability of organic beings to the highly sophisticated world of nanofabrication-enabled miniaturized biosensors. The incorporation of nanotechnology in the vast field of biosensing has led to the development of novel sensors and sensing mechanisms, as well as an increase in the sensitivity and performance of the existing biosensors. Additionally, the nanoscale dimension further assists the development of sensors for rapid and simple detection in vivo as well as the ability to probe single biomolecules and obtain critical information for their detection and analysis. However, the major drawbacks of this include, but are not limited to, potential toxicities associated with the unavoidable release of nanoparticles into the environment, miniaturization-induced unreliability, lack of automation, and difficulty of integrating the nanostructured-based biosensors, as well as unreliable transduction signals from these devices. Although the field of biosensors is vast, we intend to explore various nanotechnology-enabled biosensors as part of this review article and provide a brief description of their fundamental working principles and potential applications. The article aims to provide the reader a holistic overview of different nanostructures which have been used for biosensing purposes along with some specific applications in the field of cancer detection and the Internet of things (IoT), as well as a brief overview of machine-learning-based biosensing.

Signal-on electrochemical aptasensors with different target-induced conformations for prostate specific antigen detection

Prostate specific antigen (PSA) has become a potential biomarker for detecting prostate cancer (PCa) in the early stage. Herein, we report a target-induced resolution for the detection of PSA sensitively and specifically by amperometric electrochemical measurements. To meet a satisfactory performance, three conformations of pre-design DNA aptamers including two stem-loop structures and a double strand structure have been investigated and compared. All of them are immobilized on gold electrode as capture probes with redox-active molecular. The mechanism of signal transduction depends on molecular recognition events involving aptamer conformational changes, thus influencing the charge transfer. A short, single-stranded DNA (ssDNA) pseudoknot forming two stem-loop structural aptamers with labeled MB at the 3' -terminus was found to posse the highest signal variation than other structure when induced by PSA due to the strong conformational change. With the optimized capture strand, the aptasensor showed the peak current increase of MB by the binding relationship between PSA and the sensor over a wide concentration range of 4 magnitude orders. The proposed aptasensor exhibited a wide detection range from 10 pg/mL to 500 ng/mL with a low detection limit of 1.24 pg/mL (S/N = 3). Moreover, the electrochemical aptasensor demonstrated good reproducibility, sensitivity, selectivity, and reliability for the detection of PSA. We also found the aptasensor had a good response in the human serum samples, making this device easy to operate for the detection of the PSA physiological concentration.

Emergent Biosensing Technologies Based on Fluorescence Spectroscopy and Surface Plasmon Resonance

The purpose of this work is to provide an exhaustive overview of the emerging biosensor technologies for the detection of analytes of interest for food, environment, security, and health. Over the years, biosensors have acquired increasing importance in a wide range of applications due to synergistic studies of various scientific disciplines, determining their great commercial potential and revealing how nanotechnology and biotechnology can be strictly connected. In the present scenario, biosensors have increased their detection limit and sensitivity unthinkable until a few years ago. The most widely used biosensors are optical-based devices such as surface plasmon resonance (SPR)-based biosensors and fluorescence-based biosensors. Here, we will review them by highlighting how the progress in their design and development could impact our daily life.

Potential of surface plasmon resonance biosensors in cancer detection

A review is made of 71 papers on surface plasmon resonance biosensors, published between 2005 and 2020, mostly in the last decade. The reviewed papers are divided into two groups, depending on the validation of the developed biosensor. Validated biosensors are briefly characterized, while those that are not validated are listed in a table. Focus is placed on applications of SPR biosensors in testing the effectiveness of cancer markers and in the discovery of new cancer markers. Seven new markers are proposed, two of them having high sensitivity and diagnostic selectivity as determined by ROC curves. Papers concerning the determination of micro RNA and large particles such as vesicles, exosomes and cancer cells are also reviewed.

Drug-Based Gold Nanoparticles Overgrowth for Enhanced SPR Biosensing of Doxycycline

In clinical chemistry, frequent monitoring of drug levels in patients has gained considerable importance because of the benefits of drug monitoring on human health, such as the avoidance of high risk of over dosage or increased therapeutic efficacy. In this work, we demonstrate that the drug doxycycline can act as an Au nanoparticle (doxy-AuNP) growth and capping agent to enhance the response of a surface plasmon resonance (SPR) biosensor for this drug. SPR analysis revealed the high sensitivity of doxy-AuNPs towards the detection of free doxycycline. More specifically, doxy-AuNPs bound with protease-activated receptor-1 (PAR-1) immobilized on the SPR sensing surface yield the response in SPR, which was enhanced following the addition of free doxy (analyte) to the solution of doxy-AuNPs. This biosensor allowed for doxycycline detection at concentrations as low as 7 pM. The study also examined the role of colloidal stability and growth of doxy-AuNPs in relation to the response-enhancement strategy based on doxy-AuNPs. Thus, the doxy-AuNPs-based SPR biosensor is an excellent platform for the detection of doxycycline and demonstrates a new biosensing scheme where the analyte can provide enhancement.

Recent progress on developing of plasmon biosensing of tumor biomarkers: Efficient method towards early stage recognition of cancer

Cancer is the second most extended disease with an improved death rate over the past several time. Due to the restrictions of cancer analysis methods, the patient's real survival rate is unknown. Therefore, early stage diagnosis of cancer is crucial for its strong detection. Bio-analysis based on biomarkers may help to overcome the problem Biosensors with high sensitivity and specificity, low-cost, high analysis speed and minimum limit of detection are practical alternatives for laboratory tests. Surface plasmon resonance (SPR) is reaching a maturity level sufficient for their application in detection and determination cancer biomarkers in clinical samples. This review discusses main concepts and performance characteristics of SPR biosensor. Mainly, it focuses on newly emerged enhanced SPR biosensors towards high-throughput and ultrasensitive screening of cancer biomarkers such as PSA, α-fetoprotein, CEA, CA125, CA 15-3, HER2, ctDNA, ALCAM, hCG, VEGF, TNF, Interleukin, IFN-γ, CD24, CD44, Ferritin, COLIV using labeling processes with focusing on the future application in biomedical research and clinical diagnosis. This article reviews current status of the field, showcasing a series of early successes in the application of SPR for clinical bioanalysis of cancer related biomolecules and detailing a series of considerations regarding sensing schemes, exposing issues with analysis in biofluids, while providing an outlook of the challenges currently associated with plasmonic materials, bioreceptor selection, microfluidics, and validation of a clinical bioassay for applying SPR biosensors to clinical samples. Research opportunities are proposed to further advance the field and transition SPR biosensors from research proof-of-concept stage to actual clinical usage.

A highly sensitive quartz crystal microbalance sensor modified with antifouling microgels for saliva glucose monitoring

Saliva glucose detection based on quartz crystal microbalance (QCM) technology has become an important research direction of non-invasive blood glucose monitoring. However, the performance of this label-free glucose sensor is heavily deteriorated by the large amount of protein contaminants in saliva. Here, we successfully achieved the direct detection of saliva glucose by endowing the microgels on the QCM chip with superior protein-resistive and glucose-sensitive properties. Specifically, the microgel networks provide plenty of boric acid binding sites to amplify the signals of targeted glucose. The amino acid layer wrapped around the microgel and crosslinking layer can effectively eliminate the impact of non-specific proteins in saliva. The designed QCM sensor has a good linearity in the glucose concentration range of 0-40 mg L^-1 in the pH range of 6.8-7.5, satisfying the physiological conditions of saliva glucose. Moreover, the sensor has excellent ability to tolerate proteins, enabling it to detect glucose in 50% human saliva. This result provides a new approach for non-invasive blood glucose monitoring based on QCM.

Functionalized gold nanoparticles with zinc finger-fused proteins as a colorimetric immunoassay platform

The quest for highly sensitive and specific detection of disease biomarkers is high, despite many advances in analysis system. Here, we present a sensitive immunoassay platform using DNA-tethered gold nanoparticles and DNA-binding zinc fingers (ZFs). Monomeric alkaline phosphatase (mAP) and human TNF-α were employed as a signal generator and a disease biomarker, respectively. Gold nanoparticles (AuNPs) were first grafted with double-stranded DNAs having specific sequences for two different types of ZFs (QNK and zif268). The alkaline phosphatase and TNF-α-specific protein binder were genetically fused to each of two different types of ZFs, respectively, followed by conjugation with the DNA-tethered AuNPs in a sequence-specific manner. The use of the functionalized AuNPs as a signal generator in a colorimetric immunoassay of TNF-α led to LOD of 120 pg/ml, showing about 161-fold higher sensitivity than a protein binder-fused mAP. The present immunoassay platform could be applied to other analytes by simply replacing a targeting moiety, allowing a versatile and reproducible colorimetric immunoassay.

Self-assembled biotin-phenylalanine nanoparticles for the signal amplification of surface plasmon resonance biosensors

A strategy for amplifying the signal of surface plasmon resonance (SPR) biosensors is reported. Biotinylated phenylalanine (Biotin-Phe) monomers were rapidly self-assembled into nanoparticles in a mild environment. The self-assembled nanoparticles were then used as the carriers of streptavidin-antibody complexes by the streptavidin-biotin interaction. The signal was amplified because of the high molecular weight of the nanoparticle-streptavidin-antibody conjugate. With prostate-specific antigen as a model analyte, the target concentration as low as 1 pg mL^-1 was readily measured. The results of the nanoparticle-enhanced SPR biosensor for analysis of serum samples are well consistent with those achieved by the enzyme-linked immunosorbent assays. This work is valuable for designing of various optical and electronic biosensors through the streptavidin-biotin interaction. Graphical abstract.

Rapid Detection of Bifidobacterium bifidum in Feces Sample by Highly Sensitive Quartz Crystal Microbalance Immunosensor

In this work, a quartz crystal microbalance (QCM) sensor has been fabricated using immunoassay for sensitive determination of Bifidobacterium bifidum. Au nanoparticle has been used for amplifying sandwich assays. The proposed immunosensor exhibited a linear detection range between 103 and 105 CFU/mL with a limit of detection of 2.1 × 102 CFU/mL. The proposed immunosensor exhibited good selectivity for B. bifidum sensing with low cross reactivity for other foodborne pathogens such as Lactobacillus acidophilus, Listeria monocytogenes, and Escherichia coli. In addition, the proposed immunosensor has been successfully used for B. bifidum detection in feces samples and food samples. The frequency decreases of 12, 17, and 10 Hz were observed from the milk samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli. The frequency decreases of 8, 15, and 7 Hz were observed from the feces samples consisting of the mixtures of L. acidophilus, L. monocytogenes, and E. coli.

A novel immunosensor for the monitoring of PSA using binding of biotinylated antibody to the prostate specific antigen based on nano-ink modified flexible paper substrate: efficient method for diagnosis of cancer using biosensing technology

Prostate cancer is the most significant reason for deaths in men, outside of lung cancer. The clinical examination of cancer proteins or biomarkers is extremely significant in early examination and monitoring of recurrence of disease after treatment. Biomarkers have expanded great clinical significance owing to their extensive spectra in the identification, elimination, early diagnosis and cure of cancer. In this work, novel, ultrasensitive sandwich-type portable bio device based on citrate-capped silver nanoparticles (Citrate-AgNPs) modified graphene quantum dots (GQDs) nano ink for detection of Prostate specific antigen (PSA) was fabricated. Functionalized cysteamine with gold nanoparticles (Cys-AuNPs) was also utilized to amplify the signal. It provides a good and high external area for the immobilization biotinylated antibody of PSA in the large amount. For the first time, citrate-AgNPs-GQDs nano ink was directly written on the cellulose paper surface (ivory sheet and photographic paper) and modified by Cys-AuNPs. So, final structure of the immunodevices was completed after including of Ab1 and PSA (antigen). The immunosensors were used for the recognition of PSA by using DPVs (differential pulse voltammetry) technique. The obtained low limit of quantification (LLOQ) of the first immunodevice (ivory sheet/Citrate AgNPs-GQDs nano-ink/CysA-Au NPs/Ab1/BSA/PSA/Ab2) was 0.07 μg/L and the linear range for the calibration plot was from 0.07 to 60 μg/L. Also, the achieved LLOQ of the second immunodevice (photographic paper/Citrate AgNPs-GQDs nano-ink/Cys-Au NPs/Ab1/BSA/PSA/Ab2) was 0.05 μg/L with the linear range of 10 to 0.05 μg/L. It is noteworthy that, proposed immunoassay was effectively utilized to the monitoring of PSA glycoprotein in unprocessed human plasma sample. Obtained results show that the constructed immunosensor is able to apply as portable bio device for the clinical analysis of PSA in human plasma samples.

Fabrication of a sensitive label free electrochemical immunosensor for detection of prostate specific antigen using functionalized multi-walled carbon nanotubes/polyaniline/AuNPs

The aim of this research is to introduce a novel label free electrochemical immunosensor based on glassy carbon electrode (GCE) modified with carboxylated carbon nanotubes (COOH-MWCNTs)/polyaniline (PANI)/gold nanoparticles (AuNPs) for the detection of prostate specific antigen (PSA). The AuNPs were utilized as a connector for PSA antibody immobilization through NH₂ groups on antibody. Investigations on modified electrode surface were performed by FT-IR spectrum, scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) to evaluate the synthesized nanocomposite and modified electrode surface. As a sensitive analytical method for the detection of PSA, differential pulse voltammetry (DPV) was employed in different ranges of antigen concentration, 1.66 ag·mL^-1 to 1.3 ng·mL^-1. In addition, the detection limit was obtained 0.5 pg·mL^-1, from the linear relationship between antigen concentration log and peak current. Also, the proposed immunosensor was carried out for the determination of PSA in human serum samples, indicating recoveries ranging from 92 to 104%. Finally, it should be noted that the reproducibility and specificity, along with the stability of the present immunosensor were examined, and satisfactory findings were obtained, thus proving it as a promising PSA immunosensor.

Colorimetric detection of Cr3+ ions in aqueous solution using poly(γ-glutamic acid)-stabilized gold nanoparticles

Detection of heavy metal ions in water is of paramount significance for environmental pollution control. Here, we report the use of γ-polyglutamic acid (γ-PGA)-stabilized gold nanoparticles (γ-PGA-Au NPs) as a probe to sense trivalent chromium (Cr3+) in aqueous solution. In our study, γ-PGA-Au NPs were first formed through one-step sodium borohydride reduction of Au salt in the presence of γ-PGA. The formed γ-PGA-Au NPs with a mean particle size of 4.6 nm show desirable colloidal stability and a significant color change from wine red to gray after exposure to Cr3+ ions, which is visible to the naked eye and easily detected by colorimetric assay using UV-vis spectrometry. The limit of detection of Cr3+ ions is 100 ppb by the naked eye and 0.2 ppb by UV-vis spectroscopy, respectively. We further show that the detection of Cr3+ using γ-PGA-Au NPs has excellent selectivity, and the recovery percentage is higher than 82% for different water samples such as lake water, river water, tap water or mineral water. Our study demonstrates that γ-PGA-Au NPs can be utilized as an efficient probe for colorimetric sensing of Cr3+ ions in a water environment.

The Principle of Nanomaterials Based Surface Plasmon Resonance Biosensors and Its Potential for Dopamine Detection

For a healthy life, the human biological system should work in order. Scheduled lifestyle and lack of nutrients usually lead to fluctuations in the biological entities levels such as neurotransmitters (NTs), proteins, and hormones, which in turns put the human health in risk. Dopamine (DA) is an extremely important catecholamine NT distributed in the central nervous system. Its level in the body controls the function of human metabolism, central nervous, renal, hormonal, and cardiovascular systems. It is closely related to the major domains of human cognition, feeling, and human desires, as well as learning. Several neurological disorders such as schizophrenia and Parkinson’s disease are related to the extreme abnormalities in DA levels. Therefore, the development of an accurate, effective, and highly sensitive method for rapid determination of DA concentrations is desired. Up to now, different methods have been reported for DA detection such as electrochemical strategies, high-performance liquid chromatography, colorimetry, and capillary electrophoresis mass spectrometry. However, most of them have some limitations. Surface plasmon resonance (SPR) spectroscopy was widely used in biosensing. However, its use to detect NTs is still growing and has fascinated impressive attention of the scientific community. The focus in this concise review paper will be on the principle of SPR sensors and its operation mechanism, the factors that affect the sensor performance. The efficiency of SPR biosensors to detect several clinically related analytes will be mentioned. DA functions in the human body will be explained. Additionally, this review will cover the incorporation of nanomaterials into SPR biosensors and its potential for DA sensing with mention to its advantages and disadvantages.

Lateral field excited quartz crystal microbalances for biosensing applications

The most common bulk acoustic wave device used in biosensing applications is the quartz crystal microbalance (QCM), in which a resonant pure shear acoustic wave is excited via electrodes on both major faces of a thin AT-cut quartz plate. For biosensing, the QCM is used to detect the capture of a target by a target-capture film. The sensitivity of the QCM is typically based solely on the detection of mechanical property changes, as electrical property change detection is limited by the electrode on its sensing surface. A modification of the QCM called the lateral field excited (LFE) QCM (LFE-QCM) has been developed with a bare sensing surface as both electrodes are now on a single face of the quartz plate. Compared to the QCM, the LFE-QCM exhibits significantly higher sensitivity to both electrical and mechanical property changes. This paper presents theoretical and experimental aspects of LFE-QCMs. In particular, the presence and strength of the usual and newfound LFE-QCM modes depend on the electrical properties of the film and/or sensing environment. This work also presents examples of experimental setups for measuring the response of an LFE-QCM, followed by results of LFE-QCMs used to detect liquid electrical and mechanical properties, chemical targets, and biological targets. Finally, details are given about the attachment of various target-capture films to the LFE-QCM surface to capture biomarkers associated with diseases such as cancer.

Bioconjugated gold nanoparticles as an efficient colorimetric sensor for cancer diagnostics

The chances of curing and reducing the adverse effect of cancer partly lie in early detection. Colorimetric sensor-based technique show promising results since the target is detected with high sensitivity but without the use of advanced/costly techniques through a simple visual color change. In most cases, gold nanoparticles (Au Nps) functionalized with biomolecules complementary to target analyte are used for colorimetric detection. The interaction of functionalized Au Nps with target analytes induce aggregation or dispersion where the color of the solution changes from red to blue or blue to red respectively, which can be visualized by the naked eyes. Such a facile technique has a high commercial viability and therefore, understanding its concept is essential. Here, some of the reported studies are discussed technically for better understanding about the invitro colorimetric detection of cancer.