Recent Progress in Nanomaterial-Based Electrochemical Biosensors for Cancer Biomarkers: A Review

Solution-Gated Thin Film Transistor Biosensor-Based SnO2 Amorphous Film for Label-Free Detection of Epithelial Cell Adhesion Molecules

Epithelial cell adhesion molecule (EpCAM) was considered to be an important marker of multiple tumors, and its high expression is closely related to the early diagnosis and treatment of tumors. At present, metal oxide semiconductors have become a key component of biosensor and bioelectronics technology. Tin oxide shows great potential for development because of its nontoxic, nonpolluting, low price, and excellent electrical properties. In this study, a novel SnO2 solution-gated thin film transistor (SGTFT) biosensor for the specific detection of EpCAM was successfully developed using SnO2 film prepared by the sol-gel method as the channel material. By selecting the optimal thickness of 100 nm SnO2 film as the channel material, the transconductance value (gm) reached 1432 μS, and the threshold voltage (Vth) remained stable at 0.288 V. In order to achieve qualitative and quantitative detection of EpCAM, SnO2 films were subjected to a specific chemical treatment to fix the aptamer. Through a specific recognition between the aptamer and EpCAM, the gate voltage changes were triggered to regulate the channel current of the device. FE-SEM, EIS, XPS, and electrical performance tests were employed to track and measure the modification process. Based on the optimizations described above, the prepared SGTFT exhibited high detection sensitivity (14.6 mV·dec-1), the limit of detection (LOD) down to 24.4 pg/mL, and the calibration curves in the range of 0.02 ng/mL-500 ng/mL for EpCAM sensing. The developed SnO2-SGTFT biosensor is anticipated to provide a new highly sensitive and specific detection platform for health monitoring and disease diagnosis.

Protein-surface interactions in nano-scale biosensors for IL-6 detection using functional monolayers

A multiscale approach is employed to investigate the interaction dynamics between interleukin-6, a key cancer biomarker, and alkyl-functionalized surfaces, with the ultimate goal of guiding biosensor design. The study integrates classical molecular dynamics, Brownian dynamics simulations, and binding experiments to explore the adsorption dynamics and energetics of IL-6 on surfaces modified with self-assembled monolayers (SAMs). The comparative analysis reveals a dramatic effect on the interaction strength of IL-6 with a SAMs comprising a mix of charged and hydrophobic ligands. Solvent accessible surface area analysis shows enhanced exposure of charged terminal groups on the mixed SAM surface. Experimental investigations using surface plasmon resonance reveal that IL-6 interactions enhance with increased charged ligand content in mixed SAMs, retaining high binding affinity even under high ionic strength conditions. Computational studies further highlight hydrophobic and electrostatic interactions as key factors driving the high affinity of IL-6 on the mixed SAMs surface. This research offers insights into optimizing surfaces for enhanced IL-6 recognition, which can be extended to other protein biomarkers, by combining experimental and computational approaches to improve biosensing performance.

Recent Advances in the Fabrication and Application of Electrochemical Paper-Based Analytical Devices

In response to growing environmental concerns, the scientific community is increasingly incorporating green chemistry principles into modern analytical techniques. Electrochemical paper-based analytical devices (ePADs) have emerged as a sustainable and efficient alternative to conventional analytical devices, offering robust applications in point-of-care testing, personalized healthcare, environmental monitoring, and food safety. ePADs align with green chemistry by minimizing reagent use, reducing energy consumption, and being disposable, making them ideal for eco-friendly and cost-effective analyses. Their user-friendly interface, alongside sensitive and selective detection capabilities, has driven their popularity in recent years. This review traces the evolution of ePADs from simple designs to complex multilayered structures that optimize analyte flow and improve detection. It also delves into innovative electrode fabrication methods, assessing key advantages, limitations, and modification strategies for enhanced sensitivity. Application-focused sections explore recent advancements in using ePADs for detecting diseases, monitoring environmental hazards like heavy metals and bacterial contamination, and screening contaminants in food. The integration of cutting-edge technologies, such as wearable wireless devices and the Internet of Things (IoT), further positions ePADs at the forefront of point-of-care testing (POCT). Finally, the review identifies key research gaps and proposes future directions for the field.

Surface-Enhanced Raman Spectroscopy and Electrochemistry: The Ultimate Chemical Sensing and Manipulation Combination

One of the lessons we learned from the COVID-19 pandemic is that the need for ultrasensitive detection systems is now more critical than ever. While sensors' sensitivity, portability, selectivity, and low cost are crucial, new ways to couple synergistic methods enable the highest performance levels. This review article critically discusses the synergetic combinations of optical and electrochemical methods. We also discuss three key application fields-energy, biomedicine, and environment. Finally, we selected the most promising approaches and examples, the open challenges in sensing, and ways to overcome them. We expect this work to set a clear reference for developing and understanding strategies, pros and cons of different combinations of electrochemical and optical sensors integrated into a single device.

Electrochemical Nanoaptasensor Based on Graphitic Carbon Nitride/Zirconium Dioxide/Multiwalled Carbon Nanotubes for Matrix Metalloproteinase-9 in Human Serum and Saliva

In this study, a nanocomposite was synthesized by incorporating graphitic carbon nanosheets, carboxyl-functionalized multiwalled carbon nanotubes, and zirconium oxide nanoparticles. The resulting nanocomposite was utilized for the modification of a glassy carbon electrode. Subsequently, matrix metalloproteinase aptamer (AptMMP-9) was immobilized onto the electrode surface through the application of ethyl-3-(3-(dimethylamino)propyl)carbodiimide hydrochloride-N-hydroxysuccinimide (EDC-NHS) chemistry. Morphological characterization of the nanomaterials and the nanocomposite was performed using field-emission scanning electron microscopy (FESEM). The nanocomposite substantially increased the electroactive surface area by 205%, facilitating enhanced immobilization of AptMMP-9. The efficacy of the biosensor was evaluated using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Under optimal conditions, the fabricated sensor demonstrated a broad range of detection from 50 to 1250 pg/mL with an impressive lower limit of detection of 10.51 pg/mL. In addition, the aptasensor exhibited remarkable sensitivity, stability, excellent selectivity, reproducibility, and real-world applicability when tested with human serum and saliva samples. In summary, our developed aptasensor exhibits significant potential as an advanced biosensing tool for the point-of-care quantification of MMP-9, promising advancements in biomarker detection for practical applications.

Proteomic-based electrochemical non-invasive biosensor for early breast cancer diagnosis

Breast cancer is the second highest cause of cancer-related mortality in women worldwide and in the United States, accounting for around 571,000 deaths per year. Early detection of breast cancer increases treatment results and the possibility of a cure. While existing diagnostic modalities such as mammography, ultrasound, and biopsy exist, some are prohibitively expensive, uncomfortable, time-consuming, and have limited sensitivity, necessitating the development of a cost-effective, rapid, and highly sensitive approach such as an electrochemical biosensor. Our research focuses on detecting breast cancer patients using the ECM1 biomarker, which has higher expression in synthetic urine. Our study has two primary objectives: (i) Diverse ECM1 protein concentrations are measured using electrochemical impedance spectroscopy and ELISA. Establishing a standard curve for the electrochemical biosensor by calibrating ECM-1 protein levels using electrochemical impedance spectroscopy. (ii) Validation of the effectiveness of the electrochemical biosensor. This aim entails testing the unknown concentration of ECM1 in the synthetic urine to ensure the efficiency of the biosensor to detect the biomarker in the early stages. The results show that the synthetic urine solution's ECM-1 detection range ranges from 1 pg/ml to 500 ng/ml. This shows that by detecting changes in ECM-1 protein levels in patient urine, the electrochemical biosensor can consistently diagnose breast cancer in its early stages or during increasing recurrence. Our findings highlight the electrochemical biosensor's efficacy in detecting early-stage breast cancer biomarkers (ECM-1) in patient urine. Further studies will be conducted with patient samples and develop handheld hardware for patient usage.

Advancement in Biosensor Technologies of 2D MaterialIntegrated with Cellulose-Physical Properties

This review paper provides an in-depth analysis of recent advancements in integrating two-dimensional (2D) materials with cellulose to enhance biosensing technology. The incorporation of 2D materials such as graphene and transition metal dichalcogenides, along with nanocellulose, improves the sensitivity, stability, and flexibility of biosensors. Practical applications of these advanced biosensors are explored in fields like medical diagnostics and environmental monitoring. This innovative approach is driving research opportunities and expanding the possibilities for diverse applications in this rapidly evolving field.

A biosensor based on graphene oxide nanocomposite for determination of carcinoembryonic antigen in colorectal cancer biomarker

Colorectal cancer is still a major global health concern, and early detection and accurate biomarker analyses are critical to its successful management. This paper describes the design and testing of a new biosensor based on a graphene oxide (GO) nanocomposite for the exact measurement of carcinoembryonic antigen (CEA), a well-known biomarker for colorectal cancer. The current study attempted to create a highly sensitive immunosensor for sensitive measurement of CEA based on a polypropylene-imine-dendrimer (PPI) and GO nanocomposite on GCE (PPI/GO/GCE). The PPI/GO nanocomposite served as an appropriate biocompatible nanostructure with a large surface area for immobilizing carcinoembryonic antigen (anti-CEA) and bovine serum albumin (BSA) molecules (BSA/anti-CEA/PPI/GO/GCE), thereby promoting the selectivity of electrochemical immunosensors, according to structural and electrochemical studies. Results showed that the BSA/anti-CEA/PPI/GO/GCE as a selective, sensitive, and stable immunosensor revealed a wide linear response from 0.001 to 2000 ng/mL, and a limit of detection of 0.3 pg/mL, which indicated comparable or better performance towards the CEA immunosensors in recent reports in the literature. This was due to the synergetic effect of the GO nanosheets and PPI with porous structure and more conductivity. Analytical results showed values of RSD (4.49%-5.04%) and recovery (90.00%-99.98%) are suitable for effective and accurate practical assessments in CEA in clinical samples. The capacity of the BSA/anti-CEA/PPI/GO/GCE to determine CEA in human blood was studied.

Protein Adsorption and Its Effects on Electroanalytical Performance of Nanocellulose/Carbon Nanotube Composite Electrodes

Protein fouling is a critical issue in the development of electrochemical sensors for medical applications, as it can significantly impact their sensitivity, stability, and reliability. Modifying planar electrodes with conductive nanomaterials that possess a high surface area, such as carbon nanotubes (CNTs), has been shown to significantly improve fouling resistance and sensitivity. However, the inherent hydrophobicity of CNTs and their poor dispersibility in solvents pose challenges in optimizing such electrode architectures for maximum sensitivity. Fortunately, nanocellulosic materials offer an efficient and sustainable approach to achieving effective functional and hybrid nanoscale architectures by enabling stable aqueous dispersions of carbon nanomaterials. Additionally, the inherent hygroscopicity and fouling-resistant nature of nanocellulosic materials can provide superior functionalities in such composites. In this study, we evaluate the fouling behavior of two nanocellulose (NC)/multiwalled carbon nanotube (MWCNT) composite electrode systems: one using sulfated cellulose nanofibers and another using sulfated cellulose nanocrystals. We compare these composites to commercial MWCNT electrodes without nanocellulose and analyze their behavior in physiologically relevant fouling environments of varying complexity using common outer- and inner-sphere redox probes. Additionally, we use quartz crystal microgravimetry with dissipation monitoring (QCM-D) to investigate the behavior of amorphous carbon surfaces and nanocellulosic materials in fouling environments. Our results demonstrate that the NC/MWCNT composite electrodes provide significant advantages for measurement reliability, sensitivity, and selectivity over only MWCNT-based electrodes, even in complex physiological monitoring environments such as human plasma.

The Method and Study of Detecting Phenanthrene in Seawater Based on a Carbon Nanotube-Chitosan Oligosaccharide Modified Electrode Immunosensor

Phenanthrene (PHE), as a structurally simple, tricyclic, polycyclic aromatic hydrocarbon (PAHs), is widely present in marine environments and organisms, with serious ecological and health impacts. It is crucial to study fast and simple high-sensitivity detection methods for phenanthrene in seawater for the environment and the human body. In this paper, a immunosensor was prepared by using a multi-wall carbon nanotube (MWCNTs)-chitosan oligosaccharide (COS) nanocomposite membrane loaded with phenanthrene antibody. The principle was based on the antibody-antigen reaction in the immune reaction, using the strong electron transfer ability of multi-walled carbon nanotubes, coupled with chitosan oligosaccharides with an excellent film formation and biocompatibility, to amplify the detection signal. The content of the phenanthrene in seawater was studied via differential pulse voltammetry (DPV) using a potassium ferricyanide system as a redox probe. The antibody concentration, pH value, and probe concentration were optimized. Under the optimal experimental conditions, the response peak current of the phenanthrene was inversely proportional to the concentration of phenanthrene, in the range from 0.5 ng·mL-1 to 80 ng·mL-1, and the detection limit was 0.30 ng·mL-1. The immune sensor was successfully applied to the detection of phenanthrene in marine water, with a recovery rate of 96.1~101.5%, and provided a stable, sensitive, and accurate method for the real-time monitoring of marine environments.

Advances in MXene-Based Electrochemical (Bio)Sensors for Neurotransmitter Detection

Neurotransmitters are chemical messengers that play an important role in the nervous system's control of the body's physiological state and behaviour. Abnormal levels of neurotransmitters are closely associated with some mental disorders. Therefore, accurate analysis of neurotransmitters is of great clinical importance. Electrochemical sensors have shown bright application prospects in the detection of neurotransmitters. In recent years, MXene has been increasingly used to prepare electrode materials for fabricating electrochemical neurotransmitter sensors due to its excellent physicochemical properties. This paper systematically introduces the advances in MXene-based electrochemical (bio)sensors for the detection of neurotransmitters (including dopamine, serotonin, epinephrine, norepinephrine, tyrosine, NO, and H₂S), with a focus on their strategies for improving the electrochemical properties of MXene-based electrode materials, and provides the current challenges and future prospects for MXene-based electrochemical neurotransmitter sensors.

Application of Various Optical and Electrochemical Nanobiosensors for Detecting Cancer Antigen 125 (CA-125): A Review

Nowadays, diagnosing early-stage cancers can be vital for saving patients and dramatically decreases mortality rates. Therefore, specificity and sensitivity in the detection of cancer antigens should be elaborately ensured. Some early-stage cancers can be diagnosed via detecting the cancer antigen CA-125, such as ovarian cancer, and required treatments can be applied more efficiently. Thus, detection of CA-125 by employing various optical or electrochemical biosensors is a preliminary and crucial step to treating cancers. In this review, a diverse range of optical and electrochemical means of detecting CA-125 are reviewed. Furthermore, an applicable comparison of their performance and sensitivity is provided, several commercial detection kits are investigated, and their applications are compared and discussed to determine whether they are applicable and accurate enough.

Tuning gold-based surface functionalization for streptavidin detection: A combined simulative and experimental study

A rationally designed gold-functionalized surface capable of capturing a target protein is presented using the biotin–streptavidin pair as a proof-of-concept. We carried out multiscale simulations to shed light on the binding mechanism of streptavidin on four differently biotinylated surfaces. Brownian Dynamics simulations were used to reveal the preferred initial orientation of streptavidin over the surfaces, whereas classical molecular dynamics was used to refine the binding poses and to investigate the fundamental forces involved in binding, and the binding kinetics. We assessed the binding events and the stability of the streptavidin attachment through a quartz crystal microbalance with dissipation monitoring (QCM-D). The sensing element comprises of biotinylated polyethylene glycol chains grafted on the sensor’s gold surface via thiol-Au chemistry. Finally, we compared the results from experiments and simulations. We found that the confined biotin moieties can specifically capture streptavidin from the liquid phase and provide guidelines on how to exploit the microscopic parameters obtained from simulations to guide the design of further biosensors with enhanced sensitivity.

Recent Progress in Biosensors for Detection of Tumor Biomarkers

Cancer is a leading cause of death worldwide, with an increasing mortality rate over the past years. The early detection of cancer contributes to early diagnosis and subsequent treatment. How to detect early cancer has become one of the hot research directions of cancer. Tumor biomarkers, biochemical parameters for reflecting cancer occurrence and progression have caused much attention in cancer early detection. Due to high sensitivity, convenience and low cost, biosensors have been largely developed to detect tumor biomarkers. This review describes the application of various biosensors in detecting tumor markers. Firstly, several typical tumor makers, such as neuron-specific enolase (NSE), carcinoembryonic antigen (CEA), prostate-specific antigen (PSA), squamous cell carcinoma antigen (SCCA), carbohydrate, antigen19-9 (CA19-9) and tumor suppressor p53 (TP53), which may be helpful for early cancer detection in the clinic, are briefly described. Then, various biosensors, mainly focusing on electrochemical biosensors, optical biosensors, photoelectrochemical biosensors, piezoelectric biosensors and aptamer sensors, are discussed. Specifically, the operation principles of biosensors, nanomaterials used in biosensors and the application of biosensors in tumor marker detection have been comprehensively reviewed and provided. Lastly, the challenges and prospects for developing effective biosensors for early cancer diagnosis are discussed.

Recent progress in the early detection of cancer based on CD44 biomarker; nano-biosensing approaches

CD44 is a cell matrix adhesion molecule overexpressed on the cell surfaces of the major cancers. CD44 as a cancer-related biomarker has an essential role in the invasion and metastasis of cancer. The detection and quantification of CD44 can provide essential information useful for clinical cancer diagnosis. In this regard, biosensors with sensitive and specific properties, give prominence to the development of CD44 detection platforms. To date, various aptamer-based sensitive-enhancers together with nanoparticles (NPs) have been combined into the biosensors systems to provide an innovative biosensing method (aptasensors/nano-aptasensors) with substantially improved detection limit. This review article discusses the recent advances in the field of biosensors, nanobiosensors, and aptasensors for the quantitative determination of CD44 and the detection of CD44-expressing cancer cells.

Graphene-Based Electrochemical Sensor for Detection of Hepatocellular Carcinoma Markers

Hepatocellular carcinoma (HCC) is a group of highly lethal malignant tumors that seriously threaten human health. The main way to improve the survival quality and reduce the mortality of HCC is early diagnosis and treatment. Therefore, it will be of great significance to explore new quantitative detection methods for HCC markers. With the rapid development of electrochemical biosensors and nanomaterials, electrochemical sensors based on graphene can detect tumor markers, with the advantages of simple operation, high detection sensitivity, and specificity. Combined with the published literature in recent years, the article briefly reviews the application of graphene-based electrochemical biosensors in the detection of HCC markers, including alpha-fetoprotein (AFP), Golgi protein-73 (GP73), exosomes, and microRNA-122 (miR-122).

Recent Progress in Nanomaterials Modified Electrochemical Biosensors for the Detection of MicroRNA

MicroRNAs (miRNAs) are important non-coding, single-stranded RNAs possessing crucial regulating roles in human body. Therefore, miRNAs have received extensive attention from various disciplines as the aberrant expression of miRNAs are tightly related to different types of diseases. Furthermore, the exceptional stability of miRNAs has presented them as biomarker with high specificity and sensitivity. However, small size, high sequence similarity, low abundance of miRNAs impose difficulty in their detection. Hence, it is of utmost importance to develop accurate and sensitive method for miRNA biosensing. Electrochemical biosensors have been demonstrated as promising solution for miRNA detection as they are highly sensitive, facile, and low-cost with ease of miniaturization. The incorporation of nanomaterials to electrochemical biosensor offers excellent prospects for converting biological recognition events to electronic signal for the development of biosensing platform with desired sensing properties due to their unique properties. This review introduces the signal amplification strategies employed in miRNA electrochemical biosensor and presents the feasibility of different strategies. The recent advances in nanomaterial-based electrochemical biosensor for the detection of miRNA were also discussed and summarized based on different types of miRNAs, opening new approaches in biological analysis and early disease diagnosis. Lastly, the challenges and future prospects are discussed.

Determination of VEGF165 using impedimetric aptasensor based on cyclohexanehexone-melem covalent-organic framework

A porous nanostructured covalent-organic framework (COF) has been prepared via condensation polymerization between the two building blocks of melem and hexaketocyclohexane octahydrate (represented as M-HO-COF). Basic characterizations revealed that the M-HO-COF network was composed of C=N and highly conjugated aromatic moieties, along with a high surface area, large pore size, remarkable electrochemical activity, and strong bioaffinity toward aptamer strands. Given that the vascular endothelial growth factor 165 (VEGF₁₆₅)-targeted aptamer was stably anchored over M-HO-COF via weak intermolecular forces, the prepared M-HO-COF network exhibited great potential as a sensitive and selective platform for the impedimetric VEGF₁₆₅ aptasensor. Consequently, the M-HO-COF-based aptasensor displayed an ultralow limit of detection of 0.18 fg mL^-1 within a wide range of VEGF₁₆₅ concentrations from 1 fg mL^-1 to 10 ng mL^-1. Considering its strong fluorescence performance, excellent biocompatibility, and small nanosheet-like structure, the obtained COF-based aptasensor showed a superior sensing performance and regeneration capability after 7 regeneration cycles for the detection of osteosarcoma cells (K7M2 cells), which overexpressed with VEGF₁₆₅, with a low limit of detection of 49 cells mL^-1. For real f human serum samples, the obtained COF-based aptasensor exhibits acceptable mean apparent recoveries of 97.41% with a relative standard deviation of 4.60%. Furthermore, the proposed bifunctional aptasensor for the detection VEGF₁₆₅ and K7M2 cells exhibited good stability, appropriate selectivity toward other biomarkers or normal cells, acceptable reproducibility, and applicability. A bifunctional sensing system was constructed for detecting osteosarcoma cells (K7M2 cells) and VEGF₁₆₅ based on the a porous nanostructured covalent-organic framework (M-HO-COF) via condensation polymerization between melem and hexaketocyclohexane octahydrate. The M-HO-COF-based aptasensor displayed ultralow detection limit of 0.18 fg mL^-1 toward VEGF₁₆₅ and 49 cell mL^-1 for K7M2 cells with high selectivity, acceptable reproducibility, and good stability.

Nanotechnology in ovarian cancer: Diagnosis and treatment

To overcome the drawbacks of conventional delivery, this review spotlights a number of nanoscale drug delivery systems, including nanoparticles, liposomes, nano micelles, branched dendrimers, nanocapsules, and nanostructured lipid formulations for the targeted therapy of ovarian cancer. These nanoformulations offer numerous advantages to promote therapeutic drug delivery such as nontoxicity, biocompatibility, good biodegradability, increased therapeutic impact than free drugs, and non-inflammatory effects. Importantly, the development of specific ligands functionalized nanoformulations enable preferential targeting of ovarian tumors and eventually amplify the therapeutic potential compared to nonfunctionalized counterparts. Ovarian cancer is typically identified by biomarker assessment such as CA125, HE4, Mucin 1, and prostatic. There is, nevertheless, a tremendous demand for less costly, faster, and compact medical tools, both for timely detection and ovarian cancer control. This paper explored multiple types of tumor marker-based on nanomaterial biosensors. Initially, we mention different forms of ovarian cancer biomarkers involving CA125, human epididymis protein 4 (HE4), mucin 1 (MUC1), and prostate. It is accompanied by a brief description of new nanotechnology methods for diagnosis. Nanobiosensors for evaluating ovarian cancer biomarkers can be categorized based on electrochemical, optical, paper-based, giant magnetoresistive, and lab-on-a-chip devices.

Engineering strategies for enhancing the performance of electrochemical paper-based analytical devices

Applications of electrochemical detection methods in microfluidic paper-based analytical devices (μPADs) has revolutionized the area of point-of-care (POC) testing towards highly sensitive and selective quantification of various (bio)chemical analytes in a miniaturized, low-coat, rapid, and user-friendly manner. Shortly after the initiation, these relatively new modulations of μPADs, named as electrochemical paper-based analytical devices (ePADs), gained widespread popularity within the POC research community thanks to the inherent advantages of both electrochemical sensing and usage of paper as a suitable substrate for POC testing platforms. Even though general aspects of ePADs such as applications and fabrication techniques, have already been reviewed multiple times in the literature, herein, we intend to provide a critical engineering insight into the area of ePADs by focusing particularly on the practical strategies utilized to enhance their analytical performance (i.e. sensitivity), while maintaining the desired simplicity and efficiency intact. Basically, the discussed strategies are driven by considering the parameters potentially affecting the generated electrochemical signal in the ePADs. Some of these parameters include the type of filter paper, electrode fabrication methods, electrode materials, fluid flow patterns, etc. Besides, the limitations and challenges associated with the development of ePADs are discussed, and further insights and directions for future research in this field are proposed.

Electron Spin Resonance Evidence for Electro-generated Hydroxyl Radicals

Electro-generated hydroxyl radicals (•OH) are of fundamental importance to the electrochemical advanced oxidation process (EAOP). Radical-specific electron spin resonance (ESR) evidence is still lacking in association with the direct electron transfer (DET) reaction of spin trap (e.g., 5,5-dimethyl-1-pyrroline-N-oxide; DMPO) and side reactions of the DMPO-OH adduct in the strongly oxidative environment offered by anodic polarization. Herein, we showed ESR identification of electro-generated •OH in EAOP based on the principle of kinetic selection. Excessive addition of a DMPO agent and fast spin trapping allowed suitable kinetic conditions to be set for effective spin trapping of electro-generated •OH and subsequent ESR identification. Otherwise, interferential triplet signals would emerge due to formation of paramagnetic dimer via dehydrogenation, DET oxidation, and dimerization reactions of the DMPO-OH adduct. The results demonstrate that •OH formation during spin-trapping on the titanium suboxide (TiSO) anode could be quantified as 47.84 ± 0.44 μM at current density of 10 mA cm^-2. This value revealed a positive dependence on electrolysis time, current density, and anode potential. The effectiveness of ESR measurements was verified by the results obtained with the terephthalic acid probe. The ESR identification not only provides direct evidence for electro-generated •OH from a fundamental point of view, but also suggests a strategy to screen effective anode materials.

An electrochemical sensor based on gold nanoparticles-functionalized reduced graphene oxide screen printed electrode for the detection of pyocyanin biomarker in Pseudomonas aeruginosa infection

Multidrug resistant Pseudomonas aeruginosa (P. aeruginosa) is known to be a problematic bacterium for being a major cause of opportunistic and nosocomial infections. In this study, reduced graphene oxide decorated with gold nanoparticles (AuNPs/rGO) was utilized as a new sensing material for a fast and direct electrochemical detection of pyocyanin as a biomarker of P. aeruginosa infections. Under optimal condition, the developed electrochemical pyocyanin sensor exhibited a good linear range for the determination of pyocyanin in phosphate-buffered saline (PBS), human saliva and urine at a clinically relevant concentration range of 1-100 μM, achieving a detection limit of 0.27 μM, 1.34 μM, and 2.3 μM, respectively. Our developed sensor demonstrated good selectivity towards pyocyanin in the presence of interfering molecule such as ascorbic acid, uric acid, NADH, glucose, and acetylsalicylic acid, which are commonly found in human fluids. Furthermore, the developed sensor was able to discriminate the signal with and without the presence of pyocyanin directly in P. aeruginosa culture. This proposed technique demonstrates its potential application in monitoring the presence of P. aeruginosa infection in patients.

Recent advances in aptamer-based sensors for breast cancer diagnosis: special cases for nanomaterial-based VEGF, HER2, and MUC1 aptasensors

Cancer is one of the most common and important diseases with a high mortality rate. Breast cancer is among the three most common types of cancer in women, and the mortality rate has reached 0.024% in some countries. For early-stage preclinical diagnosis of breast cancer, sensitive and reliable tools are needed. Today, there are many types of biomarkers that have been identified for cancer diagnosis. A wide variety of detection strategies have also been developed for the detection of these biomarkers from serum or other body fluids at physiological concentrations. Aptamers are single-stranded DNA or RNA oligonucleotides and promising in the production of more sensitive and reliable biosensor platforms in combination with a wide range of nanomaterials. Conformational changes triggered by the target analyte have been successfully applied in fluorometric, colorimetric, plasmonic, and electrochemical-based detection strategies. This review article presents aptasensor approaches used in the detection of vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2), and mucin-1 glycoprotein (MUC1) biomarkers, which are frequently studied in the diagnosis of breast cancer. The focus of this review article is on developments of the last decade for detecting these biomarkers using various sensitivity enhancement techniques and nanomaterials.

Enhancing the Sensitivity of Biotinylated Surfaces by Tailoring the Design of the Mixed Self-Assembled Monolayer Synthesis

Thiolated self-assembled monolayers (SAMs) are typically used to anchor on a gold surface biomolecules serving as recognition elements for biosensor applications. Here, the design and synthesis of N-(2-hydroxyethyl)-3-mercaptopropanamide (NMPA) in biotinylated mixed SAMs is proposed as an alternative strategy with respect to on-site multistep functionalization of SAMs prepared from solutions of commercially available thiols. In this study, the mixed SAM deposited from a 10:1 solution of 3-mercaptopropionic acid (3MPA) and 11-mercaptoundecanoic acid (11MUA) is compared to that resulting from a 10:1 solution of NMPA:11MUA. To this end, surface plasmon resonance (SPR) and attenuated total reflectance infrared (ATR-IR) experiments have been carried out on both mixed SAMs after biotinylation. The study demonstrated how the fine tuning of the SAM features impacts directly on both the biofunctionalization steps, i.e., the biotin anchoring, and the biorecognition properties evaluated upon exposure to streptavidin analyte. Higher affinity for the target analyte with reduced nonspecific binding and lower detection limit has been demonstrated when NMPA is chosen as the more abundant starting thiol. Molecular dynamics simulations complemented the experimental findings providing a molecular rationale behind the performance of the biotinylated mixed SAMs. The present study confirms the importance of the functionalization design for the development of a highly performing biosensor.

Review on Sensing Applications of Perovskite Nanomaterials

Recently, perovskite-based nanomaterials are utilized in diverse sustainable applications. Their unique structural characteristics allow researchers to explore functionalities towards diverse directions, such as solar cells, light emitting devices, transistors, sensors, etc. Many perovskite nanomaterial-based devices have been demonstrated with extraordinary sensing performance to various chemical and biological species in both solid and solution states. In particular, perovskite nanomaterials are capable of detecting small molecules such as O2, NO2, CO2, etc. This review elaborates the sensing applications of those perovskite materials with diverse cations, dopants and composites. Moreover, the underlying mechanisms and electron transport properties, which are important for understanding those sensor performances, will be discussed. Their synthetic tactics, structural information, modifications and real time sensing applications are provided to promote such perovskite nanomaterials-based molecular designs. Lastly, we summarize the perspectives and provide feasible guidelines for future developing of novel perovskite nanostructure-based chemo- and biosensors with real time demonstration.

Bio-assay of the non-amidated progastrin-derived peptide (G17-Gly) using the tailor-made recombinant antibody fragment and phage display method: a biomedical analysis

In this research, four novel and sensitive immunosensors for electrochemical determination of G17-Gly were designed based on signal amplification and tailor-made recombinant antibody technology. Anti-G17-Gly antibody fragments (i.e. scFv and VL specific to the N- and C-terminal of G17-Gly) were immobilized onto a polymeric nanocomposite comprising poly cetyl trimethyl ammonium bromide (P(CTAB)) as the conductive matrix, chitosan (CS) as a biocompatible agent and gold nanoparticles (AuNPs) as the signal amplification element. The high surface area provided by AuNPs and the small size of scFv/VL establish the basis for immobilizing a high amount of the anti-G17-Gly on the surface of the electrode for detecting G17-Gly in human plasma samples. Under optimal conditions, the designed immunosensors provide an excellent analytical capability for detecting and determining G17-Gly in human plasma samples with a linear range from 0.5 mM to 0.05 pM and a LLOQ of 0.05 pM. The sensitivity order of the immunosensors was Ag/2-mercaptoethanol/phage displaying scFv/P(CTAB-CS)-AuNP/GE, Ag/2-mercaptoethanol/phage displaying VL/P(CTAB-CS)-AuNP/GE, Ag/BSA/scFv/P(CTAB-CS)-AuNP/GE, and Ag/BSA/VL/P(CTAB-CS)-AuNP/GE. The aforementioned characteristics demonstrate that the proposed immune-devices can be used in biological and clinical diagnosis as reliable tools for identifying different oncobiomarkers.

Ultrasensitive Fluorescent miRNA Biosensor Based on a "Sandwich" Oligonucleotide Hybridization and Fluorescence Resonance Energy Transfer Process Using an Ln(III)-MOF and Ag Nanoparticles for Early Cancer Diagnosis: Application of Central Composite Design

Herein, a novel, rapid, highly sensitive, and selective fluorescent biosensor is presented, which is designed based on "sandwich-type" hybridization of oligonucleotides and the fluorescence resonance energy transfer (FRET) strategy. It senses and determines the MicroRNA-155 (miRNA-155) expression levels as a cancer biomarker. In this study, a modified La(III)-metal-organic framework(MOF) and silver nanoparticles (Ag NPs) were used as the energy donor-acceptor pairs in fluorescence quenching through the FRET process. La(III)-MOF was synthesized and then modified by glutaraldehyde as a cross-linking agent. The Ag NPs were also prepared, and then, the surface of both was conjugated with different 5'-amino-labeled ssDNA strands (aptamers). These prepared nanoprobes were characterized by various physicochemical techniques such as X-ray diffraction, energy-dispersive X-ray spectrometry, Fourier transform infrared, field emission scanning electron microscopy, UV-vis spectroscopy, elemental mapping, and gel electrophoresis. To optimize the detection conditions, several factors affecting biosensor performance were assessed by one variable-at-a-time and central composite design methods. Under optimum conditions, this "turn-off" fluorescent biosensor could detect and determine as low as 0.04 ppb (ng. mL^-1) or 5.5 fM of the miRNA-155 biomarker. Therefore, this biosensor provides highly promising potential for lung and breast cancer diagnosis.

Biosensors for Personal Mobile Health: A System Architecture Perspective

Advances in mobile biosensors, integrating developments in materials science and instrumentation, are fueling an expansion in health data being collected and analyzed in decentralized settings. For example, semiconductor-based sensors are enabling measurement of vital signs, and microfluidic-based sensors are enabling measurement of biochemical markers. As biosensors for mobile health are becoming increasingly paired with smart devices, it will become critical for researchers to design biosensors - with appropriate functionalities and specifications - to work seamlessly with accompanying connected hardware and software. This article describes recent research in biosensors, as well as current mobile health devices in use, as classified into four distinct system architectures that take into account the biosensing and data processing functions required in personal mobile health devices. We also discuss the path forward for integrating biosensors into smartphone-based mobile health devices.

Highly sensitive and selective electrochemical immunosensors by substrate-enhanced electroless deposition of metal nanoparticles onto three-dimensional graphene@Ni foams

In this study, we have for the first time preformed the facile substrate-enhanced electroless deposition (SEED) of metal nanoparticles onto monolithic graphene@Ni foams for construction of disposable three-dimensional (3D) electrochemical immunosensors. Specifically, we firstly used the SEED method to deposit gold nanoparticles (AuNPs) onto the graphene@Ni foam for immobilization of antibody (Ab₁). This is followed by a second step SEED deposition to produce silver nanoparticles (AgNPs) for electrochemical stripping detection. Using α-fetoprotein antigen (AFP) as a module analyte, the newly-developed sensor showed a wide linear response, ranging from 5.0 pg/mL to 5.0 ng/mL and a low detection limit down to 2.3 pg/mL. The newly-developed 3D-immunosensor is sensitive, reliable, and easy to be fabricated, showing great potential for clinic applications.

Electrochemical Characterization of Mancozeb Degradation for Wastewater Treatment Using a Sensor Based on Poly (3,4-ethylenedioxythiophene) (PEDOT) Modified with Carbon Nanotubes and Gold Nanoparticles

Mancozeb is a worldwide fungicide used on a large scale in agriculture. The active component and its main metabolite, ethylene thiourea, has been related to health issues. Robust, fast, and reliable methodologies to quantify its presence in water are of great importance for environmental and health reasons. The electrochemical evaluation of mancozeb using a low-cost electrochemical electrode modified with poly (3,4-ethylene dioxythiophene), multi-walled carbon nanotubes, and gold nanoparticles is a novel strategy to provide an in-situ response for water pollution from agriculture. Additionally, the thermal-, electrochemical-, and photo-degradation of mancozeb and the production of ethylene thiourea under controlled conditions were evaluated in this research. The mancozeb solutions were characterized by electrochemical oxidation and ultraviolet-visible spectrophotometry, and the ethylene thiourea concentration was measured using ultra-high-performance liquid chromatography high-resolution mass spectrometry. The degradation study of mancozeb may provide routes for treatment in wastewater treatment plants. Therefore, a low-cost electrochemical electrode was fabricated to detect mancozeb in water with a robust electrochemical response in the linear range as well as a quick response at a reduced volume. Hence, our novel modified electrode provides a potential technique to be used in environmental monitoring for pesticide detection.

Graphene-based biosensors for the detection of prostate cancer protein biomarkers: a review

Prostate cancer (PC) is the sixth most common cancer type in the world, which causes approximately 10% of total cancer fatalities. The detection of protein biomarkers in body fluids is the key topic for the diagnosis and prognosis of PC. Highly sensitive screening of PC is the most effective approach for reducing mortality. Thus, there are a growing number of literature that recognizes the importance of new technologies for early diagnosis of PC. Graphene is playing an important role in the biosensor field with remarkable physical, optical, electrochemical and magnetic properties. Many recent studies demonstrated the potential of graphene materials for sensitive detection of protein biomarkers. In this review, the graphene-based biosensors toward PC analysis are mainly discussed in two groups: Firstly, novel biosensor interfaces were constructed through the modification of graphene materials onto sensor surfaces. Secondly, ingenious signal amplification strategies were developed using graphene materials as catalysts or carriers. Graphene-based biosensors have exhibited remarkable performance with high sensitivities, wide detection ranges, and long-term stabilities.

Lectin biosensors in cancer glycan biomarker detection

Cancer has high incidence and it will continue to increase over the next decades. Detection and quantification of cancer-associated biomarkers is frequently carried out for diagnosis, prognosis and treatment monitoring at various disease stages. It is well-known that glycosylation profiles change significantly during oncogenesis. Aberrant glycans produced during tumorigenesis are, therefore, valuable molecules for detection and characterization of cancer, and for therapeutic design and monitoring. Although glycoproteomics has benefited from the development of analytical tools such as high performance liquid chromatography, two-dimensional gel and capillary electrophoresis and mass spectrometry, these approaches are not well suited for rapid point-of-care (POC) testing easily performed by medical staff. Lectins are biomolecules found in nature with specific affinities toward particular glycan structures and bind them thus forming a relatively strong complex. Because of this characteristic, lectins have been used in analytical techniques for the selective capture or separation of certain glycans in complex samples, namely, in lectin affinity chromatography, or to characterize glycosylation profiles in diverse clinical situations, using lectin microarrays. Lectin-based biosensors have been developed for the detection of specific aberrant and cancer-associated glycostructures to aid diagnosis, prognosis and treatment assessment of these patients. The attractive features of biosensors, such as portability and simple use make them highly suitable for POC testing. Recent developments in lectin biosensors, as well as their potential and pitfalls in cancer glycan biomarker detection, are presented in this chapter.

Solvothermal Preparation and Electrochemical Characterization of Cubic ZrO₂ Nanoparticles/Highly Reduced Graphene (HRG) based Nanocomposites

A single-step solvothermal approach to prepare stabilized cubic zirconia (ZrO₂) nanoparticles (NPs) and highly reduced graphene oxide (HRG) and ZrO₂ nanocomposite (HRG@ZrO₂) using benzyl alcohol as a solvent and stabilizing ligand is presented. The as-prepared ZrO₂ NPs and the HRG@ZrO₂ nanocomposite were characterized using transmission electron microscopy (TEM) and X-ray diffraction (XRD), which confirmed the formation of ultra-small, cubic phase ZrO₂ NPs with particle sizes of ~2 nm in both reactions. Slight variation of reaction conditions, including temperature and amount of benzyl alcohol, significantly affected the size of resulting NPs. The presence of benzyl alcohol as a stabilizing agent on the surface of ZrO₂ NPs was confirmed using various techniques such as ultraviolet-visible (UV-vis), Fourier-transform infrared (FT-IR), Raman and XPS spectroscopies and thermogravimetric analysis (TGA). Furthermore, a comparative electrochemical study of both as-prepared ZrO₂ NPs and the HRG@ZrO₂ nanocomposites is reported. The HRG@ZrO₂ nanocomposite confirms electronic interactions between ZrO₂ and HRG when compared their electrochemical studies with pure ZrO₂ and HRG using cyclic voltammetry (CV).