Gold Nano/Micro-Islands Overcome the Molecularly Imprinted Polymer Limitations to Achieve Ultrasensitive Protein Detection

Potential-resolved electrochemiluminescent immunoassay based on dual co-reactants regulation

Multi-signal-based self-calibrating biosensors have become a research focus due to their superior accuracy and sensitivity in recent years. Herein, the potential-resolved differential ECL immunoassay based on dual co-reactants regulation was developed. Meso-tetra(4-carboxyphenyl)porphyrin (TCPP) functionalized zirconium dioxide (ZrO2) composites (TCPP-ZrO2) was first synthesized using TCPP as the luminophore and ZrO2 as the enhancer and stabilizer. The organic-inorganic hybrid structure of TCPP-ZrO2 limits the intramolecular motion of TCPP and accelerates the production of reactive radicals of co-reactants, thus exhibiting excellent ECL intensity and stability. Then, the potential-resolved ECL properties of TCPP-ZrO2 regulated only by two co-reactants were explored. On this basis, a differential ECL immunosensor was constructed for the sensitive and accurate determination of heart-fatty acid binding protein (hFABP) using 2-(dibutylamino)ethanol modified gold nanoparticles (DBAE@Au) as labels (ECL-1, +1.3 V) and ECL-2 (-1.3 V) triggered by potassium persulfate (K2S2O8) as the internal reference. In the presence of hFABP, DBAE@Au was captured by the sensing interface to generate ECL-1 and consume K2S2O8, leading to a significant decrease of ECL-2. According to the intensity difference between ECL-2 and ECL-1, the detection of hFABP was achieved with a low detection limit and a wide linear range. The proposed differential ECL immunosensor has been applied in testing human serum samples with satisfactory results, demonstrating its promising applications for clinical diagnosis.

Visible-Light Photo-Iniferter Polymerization of Molecularly Imprinted Polymers for Direct Integration with Nanotransducers

Molecularly Imprinted Polymers (MIPs) have gained prominence as synthetic receptors, combining simplicity of synthesis with robust molecular recognition akin to antibodies and enzymes. One of their main application areas is chemical sensing. However, direct integration of MIPs with nanostructured transducers, crucial for enhancing sensing capabilities and broadening MIPs sensing applications, remains limited. This limitation mainly arises from the need for precise control over the MIP features (such as thickness) during deposition on nanostructured transducers. This work explores the potential of depositing MIPs directly onto nanostructured transducers via controlled radical photopolymerization, focusing on nanoporous silica (PSiO2) with pore sizes of 40 nm and aspect ratio exceeding 100 as an interferometric optical nanotransducer. Leveraging the covalent attachment of a photo-iniferter agent onto the PSiO2 surface, we achieved effective control over the polymerization process, resulting in the deposition of thin and uniform MIP layers on PSiO2. As a case study, we developed an MIP-based PSiO2 optical sensor for propranolol, used as the template molecule, showcasing excellent linearity, a low detection limit, and efficacy in real matrices such as tap water. The results further demonstrate the sensor selectivity for the target molecule, along with its reusability and stability for at least 60 days.

Formation of molecularly imprinted polymers: Strategies applied for the removal of protein template (review)

The key step in the entire molecularly imprinted polymer (MIP) preparation process is the formation of the complementary cavities in the polymer matrix through the template removal process. The template is removed using chemical treatments, leaving behind selective binding sites for target molecules within the polymer matrix. Other MIP preparation steps include mixing monomers and template molecules in the appropriate solvent(s), monomer-template complex equilibration, and polymerisation of the monomers around the template. However, template removal is the most important among all the preparation steps because the final structure, which can be accepted and recognised as the MIP, is obtained only after the template removal. A thorough analysis of the studies dedicated to MIP applications demonstrates that this MIP preparation step, namely the template removal, is relatively understudied. MIP template removal is especially challenging in the synthesis, where the molecular template is a macromolecule such as a protein. This review aims to provide a deliberate, systematic, and consistent overview of protein removal as the MIP template molecules. The most prevalent template removal methods are outlined for removing protein templates from electrochemically synthesised MIPs, particularly thin layers on electrodes used in electrochemical sensors. Five protein template removal approaches involving chemical treatment are highlighted, which include the utilisation of (i) chaotropic agents, (ii) salt, (iii) acidic cleavage, (iv) alkaline, and finally, (v) proteolytic treatment focusing on studies conducted over the past decade. In addition, we discuss the interactions driving the removal of protein templates in each approach and associated challenges. This review provides insights into MIPs protein template removal strategies while highlighting the prevalent issue of this understudied step of template removal.

MXene Nanoconfinement of SAM-Modified Molecularly Imprinted Electrochemical Biosensor for Point-of-Care Monitoring of Carcinoembryonic Antigen

The high rate of cancer worldwide and the heavy costs imposed on governments and humanity have always motivated researchers to develop point-of-care (POC) biosensors for easy diagnosis and monitoring of cancer treatment. Herein, we report on a label-free impedimetric biosensor based on Ti3C2Tx MXene and imprinted ortho-phenylenediamine (o-PD) for the detection of carcinoembryonic antigen (CEA), a biomarker for various cancers surveillance, especially colorectal cancer (CRC). Accordingly, MXene was drop-casted on the surface of a disposable silver electrode to increase the sensitivity and create high-energy nanoareas on the surface, which are usable for protein immobilization and detection. A self-assembled monolayer (SAM) was exploited for oriented CEA immobilization on the MXene-modified electrode. The monomer-protein interaction and successful protein removal were confirmed by molecular docking and atomic force microscopy (AFM) investigations to evaluate the quality of the fabricated molecularly imprinted polymer (MIP). Also, the role of MXene in increasing the electrical field inside the nanoareas was simulated using COMSOL Multiphysics software. A suitable limit of detection (9.41 ng/mL), an appropriate linear range of detection (10 to 100 ng/mL) in human serum, and a short detection time (10 min) resulted from the use of SAM/MIP next to MXene. This biosensor presented outstanding repeatability (97.60%) and reproducibility (98.61%). Moreover, acceptable accuracy (between 93.04 and 116.04%) in clinical serum samples was obtained compared with immunoassay results, indicating the high potential of our biosensor for real sample analysis. This biomimetic and disposable sensor provides a cost-effective method for facile and POC monitoring of cancer patients during treatment.

A reagentless molecularly imprinted polymer-based electrochemical biosensor for single-step detection of troponin I in biofluids

Reagentless molecular-imprinted polymer (MIP) electrochemical biosensors can offer the next generation of biosensing platforms for the detection of biomarkers owing to their simplicity, cost-efficacy, tunability, robustness, and accuracy. In this work, a novel combination of Prussian blue (PB), coated as an embedded redox probe on a gold working electrode (GWE), and a signal-off MIP assay has been proposed in an electrochemical format for the detection of troponin I (TnI) in biofluids. TnI is a variant exclusive to heart muscles, and its elevated level in the bloodstream is indicative of acute myocardial infarction (AMI). The proposed lab-manufactured PB/MIP electrochemical biosensor, consisting of a simple signal-off MIP assay and a PB redox probe embedded on the GWE surface, is the first of its kind that allows for reagentless, label-free, and single-step electrochemical biosensing of proteins. The preparation steps of the biosensor were fully characterized by cyclic voltammetry (CV), atomic force microscopy (AFM), and Raman spectroscopy. Finally, the performance of the optimized biosensor was investigated through the determination of various concentrations of TnI, ranging from 10 to 100 pg mL-1 within 5 min, in serum and plasma with limits of detection less than 3.6 pg mL-1, and evaluation of selectivity towards TnI using some relevant proteins that exist in biofluids with higher concentrations.

Disease diagnosis and application analysis of molecularly imprinted polymers (MIPs) in saliva detection

Saliva has significantly evolved as a diagnostic fluid in recent years, giving a non-invasive alternative to blood analysis. A high protein concentration in saliva is delivered directly from the bloodstream, making it a "human mirror" that reflects the body's physiological state. It plays an essential role in detecting diseases in biomedical and fitness monitoring. Molecularly imprinted polymers (MIPs) are biomimetic materials with custom-designed synthetic recognition sites that imitate biological counterparts renowned for sensitive analyte detection. This paper reviews the progress made in research about MIP biosensors for detecting saliva biomarkers. Specifically, we investigate the link between saliva biomarkers and various diseases, providing detailed insights into the corresponding biosensors. Furthermore, we discuss the principles of molecular imprinting for disease diagnostics and application analysis, including recent advances in integrated MIP-sensor technologies for high-affinity analyte detection in saliva. Notably, these biosensors exhibit high discrimination, allowing for the detection of saliva biomarkers linked explicitly to chronic stress disorders, diabetes, cancer, bacterial or viral-induced illnesses, and exposure to illicit toxic substances or tobacco smoke. Our findings indicate that MIP-based biosensors match and perhaps surpass their counterparts featuring integrated natural antibodies in terms of stability, signal-to-noise ratios, and detection limits. Additionally, we highlight the design of MIP coatings, strategies for synthesizing polymers, and the integration of advanced biodevices. These tailored biodevices, designed to assess various salivary biomarkers, are emerging as promising screening or diagnostic tools for real-time monitoring and self-health management, improving quality of life.

Additively manufactured multiplexed electrochemical device (AMMED) for portable sample-to-answer detection

Portable sample-to-answer devices with applications in point-of-care settings have emerged to obviate the necessity of centralized laboratories for biomarker analysis. In this work, a smartphone-operated and additively manufactured multiplexed electrochemical device (AMMED) is presented for the portable detection of biomarkers in blood and saliva. AMMED is comprised of a customized portable potentiostat with a multiplexing feature, a 3D-printed sample collection cartridge to handle three samples of saliva and blood at the same time, a smartphone application to remotely control the potentiostat, and a 3D-printed-based multiplexed microfluidic electrochemical biosensor (test chip). Here, by employing additive manufacturing techniques, a simple, cleanroom-free, and scalable approach was proposed for the fabrication of the test chip. Moreover, these techniques can bring about easy integration of AMMED components. Additionally, the test chip can be compatible with different affinity-based bioassays which can be implemented in a multiplexed manner for detection. The AMMED components were successfully characterized in terms of electrochemical and fluidic performance. Particularly, to demonstrate the biosensing capabilities of the device, the spike protein of the SARS-CoV-2 omicron variant and a well-established aptameric assay were selected as the representative biomarker and the bioassay, respectively. The proposed device accurately and selectively detected the target of interest in a rapid (5 min) and multiplex manner with a dynamic detection range of 1-10 000 pg ml-1 in different media, and the clinical feasibility was assessed by several saliva patient samples. AMMED offers a versatile sample-to-answer platform that can be used for the detection of various biomarkers present in biofluids.

Aptamer-Based Electrochemical Microfluidic Biosensor for the Detection of Cryptosporidium parvum

Cryptosporidium parvum is a high-risk and opportunistic waterborne parasitic pathogen with highly infectious oocysts that can survive harsh environmental conditions for long periods. Current state-of-the-art methods are limited to lengthy imaging and antibody-based detection techniques that are slow, labor-intensive, and demand trained personnel. Therefore, the development of new sensing platforms for rapid and accurate identification at the point-of-care (POC) is essential to improve public health. Herein, we propose a novel electrochemical microfluidic aptasensor based on hierarchical 3D gold nano-/microislands (NMIs), functionalized with aptamers specific to C. parvum. We used aptamers as robust synthetic biorecognition elements with a remarkable ability to bind and discriminate among molecules to develop a highly selective biosensor. Also, the 3D gold NMIs feature a large active surface area that provides high sensitivity and a low limit of detection (LOD), especially when they are combined with aptamers,. The performance of the NMI aptasensor was assessed by testing the biosensor's ability to detect different concentrations of C. parvum oocysts spiked in different sample matrices, i.e., buffer, tap water, and stool, within 40 min detection time. The electrochemical measurements showed an acceptable LOD of 5 oocysts mL-1 in buffer medium, as well as 10 oocysts mL-1 in stool and tap water media, over a wide linear range of 10-100,000 oocysts mL-1. Moreover, the NMI aptasensor recognized C. parvum oocysts with high selectivity while exhibiting no significant cross-reactivity to other related coccidian parasites. The specific feasibility of the aptasensor was further demonstrated by the detection of the target C. parvum in patient stool samples. Our assay showed coherent results with microscopy and real-time quantitative polymerase chain reaction, achieving high sensitivity and specificity with a significant signal difference (p < 0.001). Therefore, the proposed microfluidic electrochemical biosensor platform could be a stepping stone for the development of rapid and accurate detection of parasites at the POC.

Molecular Complementarity of Proteomimetic Materials for Target-Specific Recognition and Recognition-Mediated Complex Functions

As biomolecules essential for sustaining life, proteins are generated from long chains of 20 different α-amino acids that are folded into unique 3D structures. In particular, many proteins have molecular recognition functions owing to their binding pockets, which have complementary shapes, charges, and polarities for specific targets, making these biopolymers unique and highly valuable for biomedical and biocatalytic applications. Based on the understanding of protein structures and microenvironments, molecular complementarity can be exhibited by synthesizable and modifiable materials. This has prompted researchers to explore the proteomimetic potentials of a diverse range of materials, including biologically available peptides and oligonucleotides, synthetic supramolecules, inorganic molecules, and related coordination networks. To fully resemble a protein, proteomimetic materials perform the molecular recognition to mediate complex molecular functions, such as allosteric regulation, signal transduction, enzymatic reactions, and stimuli-responsive motions; this can also expand the landscape of their potential bio-applications. This review focuses on the recognitive aspects of proteomimetic designs derived for individual materials and their conformations. Recent progress provides insights to help guide the development of advanced protein mimicry with material heterogeneity, design modularity, and tailored functionality. The perspectives and challenges of current proteomimetic designs and tools are also discussed in relation to future applications.

An integrated microfluidic electrochemiluminescence device for point-of-care testing of acute myocardial infarction

Heart-type fatty acid binding protein (H-FABP) is an early biomarker for acute myocardial infarction. The concentration of H-FABP in circulation sharply increases during myocardial injury. Therefore, fast and accurate detection of H-FABP is of vital significance. In this study, we developed an electrochemiluminescence device integrated with microfluidic chip (designed as m-ECL device) for on-site detection of H-FABP. The m-ECL device is consisted of a microfluidic chip that enable easy liquid handling as well as an integrated electronic system for voltage supply and photon detection. A sandwich-type ECL immunoassay strategy was employed for H-FABP detection by using Ru (bpy)₃²⁺ loaded mesoporous silica nanoparticles as ECL probes. This device can directly detect H-FABP in human serum without any pre-treatment, with a wide linear range of 1-100 ng/mL and a low limit of detection of 0.72 ng/mL. The clinical usability of this device was evaluated using clinical serum samples from patients. The results obtained from m-ECL device are well matched with those obtained from ELISA assays. We believe this m-ECL device has extensive application prospects for point-of-care testing of acute myocardial infarction.

Hierarchal polyaniline-folic acid nanostructures act as a platform for electrochemical detection of tumor cells

The fabrication of electrochemical sensing platforms for cancer monitoring by quantifying circulating tumor cells (CTCs) in blood holds promise for providing a low-cost, rapid, feasible, and safe approach for cancer diagnosis. Here, we isolate cancer cells using CoFe₂O₄ nanoparticles functionalized with folic acid and chitosan as an inexpensive magnetic nanoprobe. This electrochemical cytosensing platform was realized using polyaniline-folic acid nanohybrids with a three-dimensional hierarchical structure that presents abundant affinity sites toward overexpressed folate bioreceptors on cancer cells, in addition to retaining satisfied conductivity. Furthermore, 3D modeling and simulation of the polyaniline-folic acid structures were conducted to investigate the stable complex between aniline and folate, and the interaction between the polyaniline-folate complex and folate receptor alpha1, a bioreceptor on MCF-7 was revealed for the first time. The limit of detection was calculated to be 4 cells mL^-1 with a linear range from 50 to 10⁶ cells mL^-1.

Nanostructured-Based Optical Readouts Interfaced with Machine Learning for Identification of Extracellular Vesicles

Extracellular vesicles (EVs) are shed from cancer cells into body fluids, enclosing molecular information about the underlying disease with the potential for being the target cancer biomarker in emerging diagnosis approaches such as liquid biopsy. Still, the study of EVs presents major challenges due to their heterogeneity, complexity, and scarcity. Recently, liquid biopsy platforms have allowed the study of tumor-derived materials, holding great promise for early-stage diagnosis and monitoring of cancer when interfaced with novel adaptations of optical readouts and advanced machine learning analysis. Here, recent advances in labeled and label-free optical techniques such as fluorescence, plasmonic, and chromogenic-based systems interfaced with nanostructured sensors like nanoparticles, nanoholes, and nanowires, and diverse machine learning analyses are reviewed. The adaptability of the different optical methods discussed is compared and insights are provided into prospective avenues for the translation of the technological approaches for cancer diagnosis. It is discussed that the inherent augmented properties of nanostructures enhance the sensitivity of the detection of EVs. It is concluded by reviewing recent integrations of nanostructured-based optical readouts with diverse machine learning models as novel analysis ventures that can potentially increase the capability of the methods to the point of translation into diagnostic applications.

Recent molecularly imprinted polymers applications in bioanalysis

Molecular imprinted polymers (MIPs) as extraordinary compounds with unique features have presented a wide range of applications and benefits to researchers. In particular when used as a sorbent in sample preparation methods for the analysis of biological samples and complex matrices. Its application in the extraction of medicinal species has attracted much attention and a growing interest. This review focus on articles and research that deals with the application of MIPs in the analysis of components such as biomarkers, drugs, hormones, blockers and inhibitors, especially in biological matrices. The studies based on MIP applications in bioanalysis and the deployment of MIPs in high-throughput settings and optimization of extraction methods are presented. A review of more than 200 articles and research works clearly shows that the superiority of MIP techniques lies in high accuracy, reproducibility, sensitivity, speed and cost effectiveness which make them suitable for clinical usage. Furthermore, this review present MIP-based extraction techniques and MIP-biosensors which are categorized on their classes based on common properties of target components. Extraction methods, studied sample matrices, target analytes, analytical techniques and their results for each study are described. Investigations indicate satisfactory results using MIP-based bioanalysis. According to the increasing number of studies on method development over the last decade, the use of MIPs in bioanalysis is growing and will further expand the scope of MIP applications for less studied samples and analytes.

Advances in the Translation of Electrochemical Hydrogel-Based Sensors

Novel biomaterials for bio- and chemical sensing applications have gained considerable traction in the diagnostic community with rising trends of using biocompatible and lowly cytotoxic material. Hydrogel-based electrochemical sensors have become a promising candidate for their swellable, nano-/microporous, and aqueous 3D structures capable of immobilizing catalytic enzymes, electroactive species, whole cells, and complex tissue models, while maintaining tunable mechanical properties in wearable and implantable applications. With advances in highly controllable fabrication and processability of these novel biomaterials, the possibility of bio-nanocomposite hydrogel-based electrochemical sensing presents a paradigm shift in the development of biocompatible, "smart," and sensitive health monitoring point-of-care devices. Here, recent advances in electrochemical hydrogels for the detection of biomarkers in vitro, in situ, and in vivo are briefly reviewed to demonstrate their applicability in ideal conditions, in complex cellular environments, and in live animal models, respectively, to provide a comprehensive assessment of whether these biomaterials are ready for point-of-care translation and biointegration. Sensors based on conductive and nonconductive polymers are presented, with highlights of nano-/microstructured electrodes that provide enhanced sensitivity and selectivity in biocompatible matrices. An outlook on current challenges that shall be addressed for the realization of truly continuous real-time sensing platforms is also presented.

Hosseini I, Lu Y, Yedire SG, Mahshid SS, Tabatabaiefar MA, Liang C, Mahshid S. A Versatile Biomimic Nanotemplating Fluidic Assay for Multiplex Quantitative Monitoring of Viral Respiratory Infections and Immune Responses in Saliva and Blood

The last pandemic exposed critical gaps in monitoring and mitigating the spread of viral respiratory infections at the point-of-need. A cost-effective multiplexed fluidic device (NFluidEX), as a home-test kit analogous to a glucometer, that uses saliva and blood for parallel quantitative detection of viral infection and body's immune response in an automated manner within 11 min is proposed. The technology integrates a versatile biomimetic receptor based on molecularly imprinted polymers in a core-shell structure with nano gold electrodes, a multiplexed fluidic-impedimetric readout, built-in saliva collection/preparation, and smartphone-enabled data acquisition and interpretation. NFluidEX is validated with Influenza A H1N1 and SARS-CoV-2 (original strain and variants of concern), and achieves low detection limit in saliva and blood for the viral proteins and the anti-receptor binding domain (RBD) Immunoglobulin G (IgG) and Immunoglobulin M (IgM), respectively. It is demonstrated that nanoprotrusions of gold electrodes are essential for the fine templating of antibodies and spike proteins during molecular imprinting, and differentiation of IgG and IgM in whole blood. In the clinical setting, NFluidEX achieves 100% sensitivity and 100% specificity by testing 44 COVID-positive and 25 COVID-negative saliva and blood samples on par with the real-time quantitative polymerase chain reaction (p < 0.001, 95% confidence) and the enzyme-linked immunosorbent assay.

Electroanalytical point-of-care detection of gold standard and emerging cardiac biomarkers for stratification and monitoring in intensive care medicine - a review

Determination of specific cardiac biomarkers (CBs) during the diagnosis and management of adverse cardiovascular events such as acute myocardial infarction (AMI) has become commonplace in emergency department (ED), cardiology and many other ward settings. Cardiac troponins (cTnT and cTnI) and natriuretic peptides (BNP and NT-pro-BNP) are the preferred biomarkers in clinical practice for the diagnostic workup of AMI, acute coronary syndrome (ACS) and other types of myocardial ischaemia and heart failure (HF), while the roles and possible clinical applications of several other potential biomarkers continue to be evaluated and are the subject of several comprehensive reviews. The requirement for rapid, repeated testing of a small number of CBs in ED and cardiology patients has led to the development of point-of-care (PoC) technology to circumvent the need for remote and lengthy testing procedures in the hospital pathology laboratories. Electroanalytical sensing platforms have the potential to meet these requirements. This review aims firstly to reflect on the potential benefits of rapid CB testing in critically ill patients, a very distinct cohort of patients with deranged baseline levels of CBs. We summarise their source and clinical relevance and are the first to report the required analytical ranges for such technology to be of value in this patient cohort. Secondly, we review the current electrochemical approaches, including its sub-variants such as photoelectrochemical and electrochemiluminescence, for the determination  of important CBs highlighting the various strategies used, namely the use of micro- and nanomaterials, to maximise the sensitivities and selectivities of such approaches. Finally, we consider the challenges that must be overcome to allow for the commercialisation of this technology and transition into intensive care medicine.

Application progress of magnetic molecularly imprinted polymers chemical sensors in the detection of biomarkers

Specific recognition and highly sensitive detection of biomarkers play an essential role in identification, early diagnosis and prevention of many diseases. Magnetic molecularly imprinted polymers (MMIPs) have been widely used to capture biomimetic receptors for targets in various complex matrices due to their superior recognition ability, structural stability, and rapid separation characteristics, which overcome the existing deficiencies of traditional recognition elements such as antibodies, aptamers. The integration of MMIPs as recognition elements with chemical sensors opens new opportunities for the development of advanced analytical devices with improved selectivity and sensitivity, shorter analysis time, and lower cost. Recently, MMIPs-chemical sensors (MMIPs-CS) have made significant progress in detection, but many challenges and development spaces remain. Therefore, this review focuses on the research progress of the sensor based on biomarker detection and introduces the surface modification of the magnetic support material used to prepare high selective MMIPs, as well as the selective extraction of target biomarkers by MMIPs from the complex biological sample matrix. Based on the understanding of optical sensors and electrochemical sensors, the applications of MMIPs-optical sensors (MMIPs-OS) and MMIPs-electrochemical sensors (MMIPs-ECS) for biomarker detection were reviewed and discussed in detail. Moreover, it provides an overview of the challenges in this research area and the potential strategies for the rational design of high-performance MMIPs-CS, accelerating the development of multifunctional MMIPs-CS.

Optical cytosensors for the detection of circulating tumour cells

Blood analysis is an established approach to monitor various diseases, ranging from heart defects and diabetes to cancer. Among various tumor markers in the blood, circulating tumor cells (CTCs) have received increasing attention due to the fact that they originate directly from the tumors. Capturing and detecting CTCs represents a promising approach in cancer diagnostics and clinical management of cancers. CTCs in blood progress to self-seeding a tumour or initiating a new lesion mass. Cytosensors are biosensors intended to identify CTCs in a blood sample of cancer patients and provide information about the cancer status. Herein, we firstly discuss different detection methods of state-of-the-art optical cytosensors, including colorimetry, fluorescence, surface plasmon resonance, photoelectrochemistry and electrochemiluminescence. Then we review the significant advances made in implementing biorecognition elements and nanomaterials for the detection of cancer cells. Despite great progress in optical cytosensors, and their integration with smartphones, they have still only been explored to prototype stages. Much more effort is needed to fulfil their potential in modern cancer diagnostics and in monitoring the state of disease for cancer patients.

A nanostructured microfluidic device for plasmon-assisted electrochemical detection of hydrogen peroxide released from cancer cells

Non-invasive liquid biopsies offer hope for a rapid, risk-free, real-time glimpse into cancer diagnostics. Recently, hydrogen peroxide (H₂O₂) was identified as a cancer biomarker due to its continued release from cancer cells compared to normal cells. The precise monitoring and quantification of H₂O₂ are hindered by its low concentration and the limit of detection (LOD) in traditional sensing methods. Plasmon-assisted electrochemical sensors with their high sensitivity and low LOD make a suitable candidate for effective detection of H₂O₂, yet their electrical properties need to be improved. Here, we propose a new nanostructured microfluidic device for ultrasensitive, quantitative detection of H₂O₂ released from cancer cells in a portable fashion. The fluidic device features a series of self-organized gold nanocavities, enhanced with graphene nanosheets having optoelectrical properties, which facilitate the plasmon-assisted electrochemical detection of H₂O₂ released from human cells. Remarkably, the device can successfully measure the released H₂O₂ from breast cancer (MCF-7) and prostate cancer (PC3) cells in human plasma. Briefly, direct amperometric detection of H₂O₂ under simulated visible light illumination showed a superb LOD of 1 pM in a linear range of 1 pM-10 μM. We thoroughly studied the formation of self-organized plasmonic nanocavities on gold electrodes via surface and photo-electrochemical characterization techniques. In addition, the finite-difference time domain (FDTD) simulation of the electric field demonstrates the intensity of charge distribution at the nanocavity structure edges under visible light illumination. The superb LOD of the proposed electrode combining gold plasmonic nanocavities and graphene sheets paves the way for the development of non-invasive plasmon-assisted electrochemical sensors that can effectively detect low concentrations of H₂O₂ released from cancer cells.