A low fouling electrochemical biosensor based on the zwitterionic polypeptide doped conducting polymer PEDOT for breast cancer marker BRCA1 detection

An antifouling electrochemical sensor based on a U-shaped four-in-one peptide and poly(3,4-ethylenedioxythiophene) for vancomycin detection in fresh goat milk

Nonspecific adsorption of biomolecules (notably, proteins) and bacteria from unsterilized food may occur on sensor surfaces, which is still a challenge for food safety sensing. To achieve sensitive detection of unsterilized raw-food materials, in this study, a U-shaped four-in-one peptide with the sequence Ac-FLKLLKKLL-DOPA3-PPPPEEKDQDKEKaa that exhibited anchoring, antifouling, antibacterial, and recognition properties was designed. The peptide-modified sensor surface effectively prevented bacterial adhesion and proliferation while resisting biomolecule adsorption (signal inhibition rate as low as 0.51 % in single-protein solutions). A highly conductive polymer layer of poly(3,4-ethylenedioxythiophene) was introduced to improve the electrochemical performance before U-shaped four-in-one peptide anchoring. The proposed sensor could accurately detect vancomycin, with a wide linear range and limit of detection of 0.05-10 μg mL-1 and 2.06 ng mL-1 (S/N = 3), respectively. Satisfactory recovery rates (101.3-105.3 %) were achieved using diluted fresh goat milk.

Recent advances in PEDOT/PProDOT-derived nano biosensors: engineering nano assemblies for fostering advanced detection platforms for biomolecule detection

With the recent unprecedented emergence of a global pandemic, unknown diseases and new metabolic patterns expressing serious health issues, the requirement to develop new diagnostic tools, therapeutic solutions, and healthcare and environmental monitoring systems are significantly higher in the present situation. Considering that high sensitivity, selectivity, stability and a low limit of detection (LOD) are inevitable requirements for an ideal biosensor, the class of conducting polymers of poly(3,4-ethylenedioxythiophene) (PEDOT) and recently poly(3,4-propylenedioxythiophene) (PProDOT) materials have been demonstrated to be promising candidates for designing sensor devices. Nanostructure engineering of these polymeric materials with tunable surface properties and side chain functionalization to enable sensor probe conjugation combined with signal amplification devices such as OECTs and OFETs can fulfil the requirements of next-generation smart nano-biosensors. In this review, we analyze recent reports on PEDOT/PProDOT nanostructures and nanocomposites for developing nano-biosensors and their application in the detection of different biomarkers, environmental, toxicology, marine and aquatic monitoring, forensic and illicit drug detection, etc. In addition, we discuss the challenges associated with the design of PEDOT/PProDOT nano-biosensors and future perspectives on the exploration of novel sensor platforms, particularly PProDOT derivatives for bioelectronics and novel design strategies for next-generation smart nano-biosensors.

Fouling-Free electrochemical strategy based on vertically-aligned peptide layer for cardiac troponin I sensitive detection in human serum

BACKGROUND

Cardiac troponin I (CTnI) is demonstrated as one of the most promising disease biomarkers for early diagnosing acute myocardial infarction (AMI). To date, electrochemical immunosensors have been extensively studied in the field of cTnI determination. But highly accurate and sensitive cTnI detection by this method is still a challenge due to non-specific adsorption on electrode interfaces in complex human serum. As a result, it is necessary to develop an antifouling electrochemical immunosensor with high sensitivity for the detection of cTnI.

RESULTS

In this work, an antifouling electrochemical immunosensor was constructed based on vertically-aligned peptide layer consisting of Au nanoparticles (AuNPs) and amphiphilic CEAK16 peptide (CEAK16@AuNPs) for sensitive and accurate detection of cTnI in human serum. The vertically-aligned CEAK16@AuNPs interface provided a stable hydration layer originated from attraction of water molecules by amino acids on the hydrophilic side of the CEAK16, which effectively reduced non-specific adsorption and enhanced electron transfer rate. The cTnI immunosensor possessed great analytical performance with a wide range from 1 fg mL-1 to 1 μg mL-1 and a low detection limit of 0.28 fg mL-1 (S/N = 3). Additionally, the proposed CEAK16@AuNPs sensing interface showed excellent long-term antifouling performance and electrochemical activity that preserved 80 % of the initial signal after 20-days exposure in human serum samples. Consequently, the cTnI immunosensor displayed excellent detection accuracy compared to clinical methods and owned good selectivity, stability and reproducibility.

SIGNIFICANCE

The development of this strategy provides a versatile tool for accurate quantitative cTnI analysis in real human serum, thus helping to achieve early AMI diagnosis effectively and holding the promising potentials for other immunosensor in disease diagnosis.

Leveraging electrochemical sensors to improve efficiency of cancer detection

Electrochemical biosensors have emerged as a promising technology for cancer detection due to their high sensitivity, rapid response, low cost, and capability for non-invasive detection. Recent advances in nanomaterials like nanoparticles, graphene, and nanowires have enhanced sensor performance to allow for cancer biomarker detection, like circulating tumor cells, nucleic acids, proteins and metabolites, at ultra-low concentrations. However, several challenges need to be addressed before electrochemical biosensors can be clinically implemented. These include improving sensor selectivity in complex biological media, device miniaturization for implantable applications, integration with data analytics, handling biomarker variability, and navigating regulatory approval. This editorial critically examines the prospects of electrochemical biosensors for efficient, low-cost and minimally invasive cancer screening. We discuss recent developments in nanotechnology, microfabrication, electronics integration, multiplexing, and machine learning that can help realize the potential of these sensors. However, significant interdisciplinary efforts among researchers, clinicians, regulators and the healthcare industry are still needed to tackle limitations in selectivity, size constraints, data interpretation, biomarker validation, toxicity and commercial translation. With committed resources and pragmatic strategies, electrochemical biosensors could enable routine early cancer detection and dramatically reduce the global cancer burden.

Novel electrochemical biosensor for breast cancer detection, based on a nanocomposite of carbon nanofiber, metal-organic framework, and magnetic graphene oxide

In this study, we present the newly developed a novel microRNA biosensor based on magnetic rod carbon paste electrodes for breast cancer detection by using a relatively new MOF structure as a substrate. The major goal of manufacturing biosensors, suitable for clinical diagnostics, is to measure very low amount of microRNA 155 in complex environments. Therefore, we used a combination of different materials, including carbon nanofibers, CuBTC-AIA (CuMOF), and Fe@rGO, to improve the electrode surface-to-volume ratio and facilitate the electron transfer process. In this method, 1-pyrenebutyric acid N-hydroxysuccinimide ester was used to bind the microRNAs to the electrode surface. The hybridization process on the modified electrode surface was investigated using cyclic voltammetry, electrochemical impedance spectroscopy, and differential pulse voltammetry across the potential range, in which the accumulated hematoxylin was electroactive. Under optimal conditions, a very low detection limit of 0.08 fM and an adequate dynamic range of 0.2 fM-500 pM were achieved. The fabricated sensor was reported to be reproducible and selective when tested using different types of mismatched target sequences. And finally, the real human serum samples were used to confirm the capability of the nanobiosensor to detect microRNA 155 without any significant interference from other molecules and components.

A PEDOT enhanced covalent organic framework (COF) fluorescent probe for in vivo detection and imaging of Fe3

Simple and accurate in vivo monitoring of Fe3+ is essential for gaining a better understanding of its role in physiological and pathological processes. A novel fluorescent probe was synthesized via in situ solid-state polymerization of 3,4-ethylenedioxythiophene (PEDOT) in the pore channels of a covalent organic framework (COF). The PEDOT@COF fluorescent probe exhibited an absolute quantum yield (QY) 3 times higher than COF. In the presence of Fe3+ the PEDOT@COF 475 nm fluorescence emission, 365 nm excitation, is quenched within 180 s. Fluorescence quenching is linear with Fe3+ in the concentration range of 0-960 μM, with a detection limit of 0.82 μM. The fluorescence quenching mechanism was attributed to inner filter effect (IEF), photoinduced electron transfer (PET) and static quenching (SQE) between PEDOT@COF and Fe3+. A paper strip-based detector was designed to facilitate practical applicability, and the PEDOT@COF probe successfully applied to fluorescence imaging of Fe3+ levels in vivo. This work details a tool of great promise for enabling detailed investigations into the role of Fe3+ in physiological and pathological diseases.

Advances in the Use of Conducting Polymers for Healthcare Monitoring

Conducting polymers (CPs) are an innovative class of materials recognized for their high flexibility and biocompatibility, making them an ideal choice for health monitoring applications that require flexibility. They are active in their design. Advances in fabrication technology allow the incorporation of CPs at various levels, by combining diverse CPs monomers with metal particles, 2D materials, carbon nanomaterials, and copolymers through the process of polymerization and mixing. This method produces materials with unique physicochemical properties and is highly customizable. In particular, the development of CPs with expanded surface area and high conductivity has significantly improved the performance of the sensors, providing high sensitivity and flexibility and expanding the range of available options. However, due to the morphological diversity of new materials and thus the variety of characteristics that can be synthesized by combining CPs and other types of functionalities, choosing the right combination for a sensor application is difficult but becomes important. This review focuses on classifying the role of CP and highlights recent advances in sensor design, especially in the field of healthcare monitoring. It also synthesizes the sensing mechanisms and evaluates the performance of CPs on electrochemical surfaces and in the sensor design. Furthermore, the applications that can be revolutionized by CPs will be discussed in detail.

Electrochemical bio- and chemosensors for cancer biomarkers: Natural (with antibodies) versus biomimicking artificial (with aptamers and molecularly imprinted polymers) recognition

Electrochemical (EC) bio- and chemosensors are highly promising for on-chip and point-of-care testing (POST) devices. They can make a breakthrough in early cancer diagnosis. Most current EC sensors for cancer biomarkers' detection and determination use natural antibodies as recognition units. However, those quickly lose their biorecognition ability upon exposure to harsh environments, comprising extreme pH, humidity, temperature, etc. So-called "plastic antibodies," including aptamers and molecularly imprinted polymers (MIPs), are hypothesized to be a smart alternative to antibodies. They have attracted the interest of the sensor research community, offering a low cost-to-performance ratio with high stability, an essential advantage toward their commercialization. Herein, we critically review recent technological advances in devising and fabricating EC bio- and chemosensors for cancer biomarkers, classifying them according to the type of recognition unit used into three categories, i.e., antibody-, aptamer-, and MIP-based EC sensors for cancer biomarkers. Each sensor fabrication strategy has been discussed, from the devising concept to cancer sensing applications, including using different innovative nanomaterials and signal transduction strategies. Moreover, employing each recognition unit in the EC sensing of cancer biomarkers has been critically compared in detail to enlighten each recognition unit's advantages, effectiveness, and limitations.

An antifouling electrochemical biosensor based on chondroitin sulfate-functionalized polyaniline and DNA-peptide conjugates for cortisol determination in body fluids

An antifouling electrochemical biosensor was constructed based on chondroitin sulfate (CS)-functionalized polyaniline (CS/PANI) and DNA-peptide conjugates that is capable of assaying cortisol directly in human fluids. First, a CS-doped PANI nanocomposite (sensing substrate) was electrodeposited onto a bare glassy carbon electrode to promote electron transport, providing the sensing signal from high peak currents of PANI to improve the sensitivity of the biosensor. Dendritic DNA-peptide conjugates were assembled onto the CS/PANI by exploiting the highly specific and strong interactions between biotin and streptavidin, which amplified the sensing signals toward cortisol. The integration of the DNA-peptide conjugates into the CS/PANI nanocomposite ensured that the biosensor had a synergistic antifouling effect and was capable of detecting cortisol directly in body fluids (sweat, saliva, and tears). When assaying cortisol levels, the biosensor exhibited a linear range over the cortisol concentrations of 1 × 10-12-1 × 10-7 M and a low limit of detection (0.333 × 10-12 M). In the detection of cortisol in real samples, the relative standard deviation (RSD) of the biological samples ranged from 2.94 to 4.23%, and the recovery were calculated to be in the range 95.2-103.2%.

Strategies and Applications of Graphene and Its Derivatives-Based Electrochemical Sensors in Cancer Diagnosis

Graphene is an emerging nanomaterial increasingly being used in electrochemical biosensing applications owing to its high surface area, excellent conductivity, ease of functionalization, and superior electrocatalytic properties compared to other carbon-based electrodes and nanomaterials, enabling faster electron transfer kinetics and higher sensitivity. Graphene electrochemical biosensors may have the potential to enable the rapid, sensitive, and low-cost detection of cancer biomarkers. This paper reviews early-stage research and proof-of-concept studies on the development of graphene electrochemical biosensors for potential future cancer diagnostic applications. Various graphene synthesis methods are outlined along with common functionalization approaches using polymers, biomolecules, nanomaterials, and synthetic chemistry to facilitate the immobilization of recognition elements and improve performance. Major sensor configurations including graphene field-effect transistors, graphene modified electrodes and nanocomposites, and 3D graphene networks are highlighted along with their principles of operation, advantages, and biosensing capabilities. Strategies for the immobilization of biorecognition elements like antibodies, aptamers, peptides, and DNA/RNA probes onto graphene platforms to impart target specificity are summarized. The use of nanomaterial labels, hybrid nanocomposites with graphene, and chemical modification for signal enhancement are also discussed. Examples are provided to illustrate applications for the sensitive electrochemical detection of a broad range of cancer biomarkers including proteins, circulating tumor cells, DNA mutations, non-coding RNAs like miRNA, metabolites, and glycoproteins. Current challenges and future opportunities are elucidated to guide ongoing efforts towards transitioning graphene biosensors from promising research lab tools into mainstream clinical practice. Continued research addressing issues with reproducibility, stability, selectivity, integration, clinical validation, and regulatory approval could enable wider adoption. Overall, graphene electrochemical biosensors present powerful and versatile platforms for cancer diagnosis at the point of care.

Chemical antifouling strategies in sensors for food analysis: A review

Surface biofouling induced by the undesired nonspecific adsorption of foulants (e.g., coexisting proteins and cells) in food matrices is a major issue of sensors for food analysis, hindering their reliability and accuracy of sensing. This issue can be addressed by developing antifouling strategies to prevent or alleviate nonspecific binding. Chemical antifouling strategies involve the use of chemical modifiers (i.e., antifouling materials) to strongly hydrate the surface and reduce surface biofouling. Through appropriate immobilization approaches, antifouling materials can be tethered onto sensors to form antifouling surfaces with well-ordered structures, balanced surface charges, and appropriate surface density and thickness. A rational antifouling surface can reduce the matrix effect, simplify sample pretreatment, and improve analytical performance. This review summarizes recent developments in chemical antifouling strategies in sensing. Surface antifouling mechanisms and common antifouling materials are described, and factors that may influence the antifouling effects of antifouling surfaces and approaches incorporating antifouling materials onto sensing surfaces are highlighted. Moreover, the specific applications of antifouling sensors in food analysis are introduced. Finally, we provide an outlook on future developments in antifouling sensors for food analysis.

Advances in Electrochemical Biosensor Technologies for the Detection of Nucleic Acid Breast Cancer Biomarkers

Breast cancer is the second leading cause of cancer deaths in women worldwide; therefore, there is an increased need for the discovery, development, optimization, and quantification of diagnostic biomarkers that can improve the disease diagnosis, prognosis, and therapeutic outcome. Circulating cell-free nucleic acids biomarkers such as microRNAs (miRNAs) and breast cancer susceptibility gene 1 (BRCA1) allow the characterization of the genetic features and screening breast cancer patients. Electrochemical biosensors offer excellent platforms for the detection of breast cancer biomarkers due to their high sensitivity and selectivity, low cost, use of small analyte volumes, and easy miniaturization. In this context, this article provides an exhaustive review concerning the electrochemical methods of characterization and quantification of different miRNAs and BRCA1 breast cancer biomarkers using electrochemical DNA biosensors based on the detection of hybridization events between a DNA or peptide nucleic acid probe and the target nucleic acid sequence. The fabrication approaches, the biosensors architectures, the signal amplification strategies, the detection techniques, and the key performance parameters, such as the linearity range and the limit of detection, were discussed.

MXene supported biomimetic bilayer lipid membrane biosensor for zeptomole detection of BRCA1 gene

A biomimetic bilayer lipid membrane supported MXene based biosensor is reported for electrochemical hybridization detection of the most prevalent and potential BC biomarker BRCA1. 2D MXene nanosheet-anchored gold nanoparticle-decorated biomimetic bilayer lipid membrane (AuNP@BLM) biosensor is used for the attachment of thiolated single-stranded DNA (HS-ssDNA) targeting hybridization detection. The interaction of biomimetic bilayer lipid membrane with 2D MXene nanosheets is explored in this work for the first time. The synergistic combination of MXene and AuNP@BLM has proven to efficiently improve the detection signal to several folds. The sensor provides hybridization signals only to the complementary DNA (cDNA) sequence with a linearity range 10 zM to 1 µM and LOD of 1 zM without the need of any further amplification. The specificity of the biosensor is validated using non-complementary (ncDNA) and double base mis-match oligonucleotide DNA (dmmDNA) sequences. The sensor successfully distinguishes the signal for different target DNAs with good reproducibility indicated by the RSD value of 4.9%. Hence, we envision that the reported biosensor can be used to construct efficient diagnostic point-of-care tools based on molecular affinity interactions.

Bio-Inspired Drug Delivery Systems: From Synthetic Polypeptide Vesicles to Outer Membrane Vesicles

Nanomedicine is a broad field that focuses on the development of nanocarriers to deliver specific drugs to targeted sites. A synthetic polypeptide is a kind of biomaterial composed of repeating amino acid units that are linked by peptide bonds. The multiplied amphiphilicity segment of the polypeptide could assemble to form polypeptide vesicles (PVs) under suitable conditions. Different from polypeptide vesicles, outer membrane vesicles (OMVs) are spherical buds of the outer membrane filled with periplasmic content, which commonly originate from Gram-negative bacteria. Owing to their biodegradability and excellent biocompatibility, both PVs and OMVs have been utilized as carriers in delivering drugs. In this review, we discuss the recent drug delivery research based on PVs and OMVs. These related topics are presented: (1) a brief introduction to the production methods for PVs and OMVs; (2) a thorough explanation of PV- and OMV-related applications in drug delivery including the vesicle design and biological assessment; (3) finally, we conclude with a discussion on perspectives and future challenges related to the drug delivery systems of PVs and OMVs.

Conducting Polymers as Versatile Tools for the Electrochemical Detection of Cancer Biomarkers

The detection of cancer biomarkers has recently become an established method for the early diagnosis of cancer. The sensitive analysis of specific biomarkers can also be clinically applied for the determination of response to treatment and monitoring of disease progression. Because of the ultra-low concentration of cancer biomarkers in body fluids, diagnostic tools need to be highly sensitive and specific. Conducting polymers (CPs) are particularly known to exhibit numerous features that enable them to serve as excellent materials for the immobilization of biomolecules and the facilitation of electron transfer. Their large surface area, porosity, and the presence of functional groups provide CPs with binding sites suitable for capturing biomarkers, in addition to their sensitive and easy detection. The aim of this review is to present a comprehensive summary of the available electrochemical biosensors based on CPs and their composites for the ultrasensitive detection of selected cancer biomarkers. We have categorized the study based on different types of targeted biomarkers such as DNAs, miRNAs, proteins, enzymes, neurotransmitters and whole cancer cells. The sensitivity of their detection is enhanced by the presence of CPs, providing a limit of detection as low as 0.5 fM (for miRNA) and 10 cells (for the detection of cancer cells). The methods of multiplex biomarker detection and cell capture are indicated as the most promising category, since they furnish more accurate and reliable results. Ultimately, we discuss the available CP-based electrochemical sensors and promising approaches for facilitating cancer diagnosis and treatment.

Electrochemical determination of acetamiprid using PEDOT sensing coating functionalized with carbon quantum dots and Prussian blue nanoparticles

A dual-mode electrochemical biosensor for acetamiprid detection was proposed for the first time based on carbon quantum dots/Prussian blue (CQDs/PB)-functionalized poly(3,4-ethylenedioxythiphene) (PEDOT) nanocomposite. The nanocomposite with spherical stacking nanostructure showed high surface area, excellent catalytic ability, and cycling stability. The biosensor can be effortlessly constructed after the immobilization of acetamiprid aptamer. The concentration of acetamiprid can be determined by differential pulse voltammetry (DPV) based on its signal change deduced from the pristine PB. With the capture of acetamiprid, the response current (I-T) signal generated by hydrogen peroxide catalysis from the biosensor can also been used to establish the method for monitoring acetamiprid. The dual-mode biosensor showed a wide linear range from 10^-12 g mL^-1 to 10^-6 g mL^-1, low detection limits of 6.84 × 10^-13 g mL^-1 and 4.99 × 10^-13 g mL^-1, and ultrafast detection time of 25 s and 5 s through DPV and I-T mode, respectively. The biosensor possessed excellent selectivity and stability. More importantly, the biosensor was successfully applied to detect acetamiprid residues in vegetables, proving a promising approach for routine detection of pesticide in real samples. The biosensor based on PEDOT/CQDs/PB for acetamiprid can be effortlessly constructed through both the increase of differential pulse voltammetry (DPV) signal change deduced by the pristine PB and the decrease of the response current (I-T) signal of the reduction of hydrogen peroxide catalyzed by PEDOT/CQDs/PB.

Fabrication of a Free-Standing MWCNT Electrode by Electric Field Force for an Ultra-Sensitive MicroRNA-21 Nano-Genosensor

Abnormal expression of microRNA-21 (miR-21) is considered to be closely associated with the pathogenesis of colorectal cancer. However, great challenges do exist for the development of ultra-sensitive biosensors to detect the abnormal expression of miR-21 due to the low concentration in serum (fm level) at the early stage of colorectal cancer. Therefore, electric field force is used to rotate and rearrange random multi-walled carbon nanotubes (MWCNTs) at the microscale to improve the active sites of the electrode in this study. The free-standing MWCNTs are densely and high-orderly embedded into the bare electrode along the direction of the electric field. Compared to the bare electrode, the peak-current response of the free-standing MWCNT electrode improves by 150 times in cyclic voltammetric measurement. A nano-genosensor based on the free-standing MWCNT electrode is developed for measuring miR-21. The nano-genosensor for miR-21 shows an ultra-high sensitivity of 48.24 µA µm^-1 , a wide linear range from 0.01 × 10^-15 to 100 × 10^-12 m, and a low detection limit of 1.2 × 10^-18 m. The present nano-genosensor shows superior performance for miR-21 in human serum samples and demonstrates a potential application for the diagnosis of early stage colorectal cancer.

Highly Sensitive Detection of Carcinoembryonic Antigen via an Electrochemical Platform Fabricated by AuNPs/Streptavidin/Reduced Graphene Oxide

Tumor markers are one of the important indicators for early cancer diagnosis. As a new analytical method, electrochemical immunosensing analysis has the advantages of high sensitivity, good selectivity, and rapid detection, which is of great significance for the detection of tumor markers. In this work, an AuNP/reduced graphene oxide (AuNP/rGO) composite was synthesized. We used it for electrochemical sensor fabrication with the assistance of the biotin–streptavidin protein (SA) system to further amplify the signal to achieve sensitive detection of carcinoembryonic antigen (CEA). In addition, AuNPs have been incorporated due to their good electrical conductivity and biocompatibility, which can accelerate electron transfer at the electrode interface and improve the loading capacity to capture antibodies. The fabricated AuNPs/SA/rGO has a large working surface area and high material utilization ratio, which improves the catalytic capacity of H₂O₂ reduction and effectively amplifies the current signal. The linear range of the response current signal of the sensor toward the CEA concentration is 20 fg/ml to 200 ng/ml, and the limit of detection can achieve 6.2 fg/ml. In addition, the fabricated immunosensor has good reproducibility, selectivity, and stability.

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.

A Review of Biosensors for Detecting Tumor Markers in Breast Cancer

Breast cancer has the highest cancer incidence rate in women. Early screening of breast cancer can effectively improve the treatment effect of patients. However, the main diagnostic techniques available for the detection of breast cancer require the corresponding equipment, professional practitioners, and expert analysis, and the detection cost is high. Tumor markers are a kind of active substance that can indicate the existence and growth of the tumor. The detection of tumor markers can effectively assist the diagnosis and treatment of breast cancer. The conventional detection methods of tumor markers have some shortcomings, such as insufficient sensitivity, expensive equipment, and complicated operations. Compared with these methods, biosensors have the advantages of high sensitivity, simple operation, low equipment cost, and can quantitatively detect all kinds of tumor markers. This review summarizes the biosensors (2013-2021) for the detection of breast cancer biomarkers. Firstly, the various reported tumor markers of breast cancer are introduced. Then, the development of biosensors designed for the sensitive, stable, and selective recognition of breast cancer biomarkers was systematically discussed, with special attention to the main clinical biomarkers, such as human epidermal growth factor receptor-2 (HER2) and estrogen receptor (ER). Finally, the opportunities and challenges of developing efficient biosensors in breast cancer diagnosis and treatment are discussed.

Zwitterionic peptide-functionalized highly dispersed carbon nanotubes for efficient wastewater treatment

Multi-walled carbon nanotubes (MWCNTs) have displayed great potential as catalyst carriers due to their nanoscale structure and large specific surface area. However, their hydrophobicity and poor dispersibility in water restrict their applications in aqueous environments. Herein, the dispersibility of MWCNTs was significantly enhanced with a chimeric protein MPKE which consisted of a zwitterionic peptide unit and a mussel adhesive protein unit. The MPKE could be easily attached to MWCNTs (MPKE-MWCNTs) by a simple stirring process due to the versatile adhesion ability of mussel adhesive unit. As expected, the MPKE-MWCNTs displayed outstanding dispersibility in water (>7 months), as well as in alkaline solutions (pH = 12) and organic solvents (DMSO and ethanol) due to the hydrophilicity of the zwitterionic peptide unit. Moreover, the MPKE-MWCNTs were used as silver nanoparticle carriers for the reduction of 4-nitrophenol in wastewater, with the normalized rate constant k_nor up to 32.9 s^-1 mmol^-1. Meanwhile, they also exhibited excellent biocompatibility and antibacterial activity, which were favorable for wastewater treatment. This work provides a facile strategy for MWCNT modification, functionalization and applications in aqueous environments.

Biosensors and nanotechnology for cancer diagnosis (lung and bronchus, breast, prostate, and colon): a systematic review

The second cause of death in the world has been reported to be cancer, and it has been on the rise in recent years. As a result of the difficulties of cancer detection and its treatment, the survival rate of patients is unclear. The early detection of cancer is an important issue for its therapy. Cancer detection based on biomarkers may effectively enhance the early detection and subsequent treatment. Nanomaterial-based nanobiosensors for cancer biomarkers are excellent tools for the molecular detection and diagnosis of disease. This review reports the latest advancement and attainment in applying nanoparticles to the detection of cancer biomarkers. In this paper, the recent advances in the application of common nanomaterials like graphene, carbon nanotubes, Au, Ag, Pt, and Fe₃O₄together with newly emerged nanoparticles such as quantum dots, upconversion nanoparticles, inorganics (ZnO, MoS₂), and metal-organic frameworks for the diagnosis of biomarkers related to lung, prostate, breast, and colon cancer are highlighted. Finally, the challenges, outlook, and closing remarks are given.

Machine Learning-Reinforced Noninvasive Biosensors for Healthcare

The emergence and development of noninvasive biosensors largely facilitate the collection of physiological signals and the processing of health-related data. The utilization of appropriate machine learning algorithms improves the accuracy and efficiency of biosensors. Machine learning-reinforced biosensors are started to use in clinical practice, health monitoring, and food safety, bringing a digital revolution in healthcare. Herein, the recent advances in machine learning-reinforced noninvasive biosensors applied in healthcare are summarized. First, different types of noninvasive biosensors and physiological signals collected are categorized and summarized. Then machine learning algorithms adopted in subsequent data processing are introduced and their practical applications in biosensors are reviewed. Finally, the challenges faced by machine learning-reinforced biosensors are raised, including data privacy and adaptive learning capability, and their prospects in real-time monitoring, out-of-clinic diagnosis, and onsite food safety detection are proposed.

Porous polymeric membranes: fabrication techniques and biomedical applications

Porous polymeric membranes have shown great potential in biological and biomedical applications such as tissue engineering, bioseparation, and biosensing, due to their structural flexibility, versatile surface chemistry, and biocompatibility. This review outlines the advantages and limitations of the fabrication techniques commonly used to produce porous polymeric membranes, with especial focus on those featuring nano/submicron scale pores, which include track etching, nanoimprinting, block-copolymer self-assembly, and electrospinning. Recent advances in membrane technology have been key to facilitate precise control of pore size, shape, density and surface properties. The review provides a critical overview of the main biological and biomedical applications of these porous polymeric membranes, especially focusing on drug delivery, tissue engineering, biosensing, and bioseparation. The effect of the membrane material and pore morphology on the role of the membranes for each specific application as well as the specific fabrication challenges, and future prospects of these membranes are thoroughly discussed.

Multiplex Electrochemiluminescence Polarization Assay Based on the Surface Plasmon Coupling Effect of Au NPs and Ag@Au NPs

A novel multiplex electrochemiluminescence (ECL) polarization assay was developed to detect breast cancer-related genes BRCA1 and BRCA2 simultaneously based on the polarization characteristics of surface plasmon-coupled electrochemiluminescence (SPC-ECL). In this work, boron nitride quantum dots (BN QDs) were used as ECL emitters, and gold nanoparticles (Au NPs) and gold-coated silver nanoparticles (Ag@Au NPs) were employed as surface plasmon materials. The surface plasmon coupling resonance of different metal NPs not only enhanced the ECL intensity but also converted the isotropic emission into directional emission. This study revealed the relation between the structure of metal nanomaterials and SPC-ECL, and a high polarization-resolved sensing system was designed to detect multitarget DNA from 100 aM to 1 nM simultaneously. Polarization-based multiple ECL analysis has broad prospects in related cancer diagnosis and treatment evaluation.

"Stealth" dendrimers with encapsulation of indocyanine green for photothermal and photodynamic therapy of cancer

Poly(amido amine) dendrimers and indocyanine green have inevitable interaction with proteins and cells, which induces biological toxicity and reduces therapeutic efficacy in vivo. To overcome these shortcomings, a new drug delivery system G5MEK7C(n)-ICG with a "stealth" layer was prepared. The surface of G5MEK7C(n)-ICG was modified with double-layer super hydrophilic zwitterionic materials. In the "stealth" double-layer structure, the outer layer was consisted of zwitterionic Glu-Lys-Glu-Lys-Glu-Lys-Cys (EK7) peptide, and the inner layer was composed of amino and carboxyl groups with a ratio of 1:1. DLS results showed that the average hydrodynamic size of G5MEK7C(n)-ICG was about 25-30 nm, and the zeta potential was proven to undergo a slight charge reversal with the increasing pH values of solutions. Furthermore, G5MEK7C(n)-ICG exhibited excellent biocompatibility to red blood cells and proteins resistance. Photothermal and photodynamic experiments demonstrated that G5MEK7C(n)-ICG had a good photothermal conversion effect and generated singlet oxygen (¹O₂) under laser irradiation. The MTT and hemolysis results showed that the toxicity of G5 PAMAM was significantly reduced after modification double-layer structure. Cytotoxicity studies and flow cytometry showed G5MEK7C(70)-ICG under laser irradiation had a good effect on killing A549 cells. More importantly, the tumor inhibition rate of mice treated with G5MEK7C(70)-ICG (under laser irradiation) was 78.2% in vivo, which was higher than that of mice treated with free ICG. Compared with free ICG, G5MEK7C(70)-ICG caused less damage to the liver according to the enzyme activities of alanine aminotransferase (ALT) and aspartate aminotransferase (AST). Therefore, dendrimers modified with a zwitterionic double layer will be a promising candidate as a drug delivery system.

Advanced materials-integrated electrochemical sensors as promising medical diagnostics tools: A review

Electrochemical sensors have increasingly been linked with terms as modern biomedically effective highly selective and sensitive devices, wearable and wireless technology, portable electronics, smart textiles, energy storage, communication and user-friendly operating systems. The work brings the overview of the current advanced materials and their application strategies for improving performance, miniaturization and portability of sensing devices. It provides the extensive information on recently developed (bio)sensing platforms based on voltammetric, amperometric, potentiometric and impedimetric detection modes including portable, non-invasive, wireless, and self-driven miniaturized devices for monitoring human and animal health. Diagnostics of selected free radical precursors, low molecular biomarkers, nucleic acids and protein-based biomarkers, bacteria and viruses of today's interest is demonstrated.

Recent Advances of Conducting Polymers and Their Composites for Electrochemical Biosensing Applications

Conducting polymers (CPs) have been at the center of research owing to their metal-like electrochemical properties and polymer-like dispersion nature. CPs and their composites serve as ideal functional materials for diversified biomedical applications like drug delivery, tissue engineering, and diagnostics. There have also been numerous biosensing platforms based on polyaniline (PANI), polypyrrole (PPY), polythiophene (PTP), and their composites. Based on their unique properties and extensive use in biosensing matrices, updated information on novel CPs and their role is appealing. This review focuses on the properties and performance of biosensing matrices based on CPs reported in the last three years. The salient features of CPs like PANI, PPY, PTP, and their composites with nanoparticles, carbon materials, etc. are outlined along with respective examples. A description of mediator conjugated biosensor designs and enzymeless CPs based glucose sensing has also been included. The future research trends with required improvements to improve the analytical performance of CP-biosensing devices have also been addressed.