A review on amperometric immunoassays for tumor markers based on the use of hybrid materials consisting of conducting polymers and noble metal nanomaterials

Removal of heavy metals from the aqueous solution by nanomaterials: a review with analysing and categorizing the studies

With the development of nanotechnology and its application in various sciences, scientists have investigated the use of nanoparticles as adsorbents to remove heavy metals from aqueous solutions all over the world. So far, the results of many of these studies have been published in reputable journals. Obviously, reviewing these articles and summarizing the results of these studies from different aspects will provide new perspectives for the development of this technology for heavy metals removal from water. So the current study was performed to review the results of the published studies between 1/January/1980 to 1/January/2022. The focus of the study is on the analysis of these studies and their classification. In addition, a more detailed investigation was carried out. Among the 5155 articles, 576 articles were included based on Cochrane protocols. Results show that most of the studies (90.8%) were conducted on a laboratory scale and used synthetic solutions. Most studies were performed for Pb, Cd and Cu, removal respectively. Compared to other countries, authors with affiliation from China and Iran have published more articles. The ranking of the use of various nanomaterials were: nanocomposites > metal oxide nanomaterials > metal-based nanomaterials > carbon-based nanomaterials > dendrimers, with the wide range of sizes from less than 10 nm to several hundreds of nanometers. The required amount of carbon-based nanoparticles to remove many heavy metals were lower than other nanoparticles. In most studies, pH ≤ 7 has been reported as optimal. Most studies have been followed pseudo second-order and pseudo first-order reactions and have been more agreement with Langmuir and Freundlich adsorption isotherms respectively. The results of studies show that the synthesis and optimization of new nanomaterials can be considered as a new and competitive technology. However, more studies are needed to investigate the removal of heavy metals in real samples and to overcome some challenges in the full-scale application.

An electrochemical aptasensor for highly sensitive detection of CEA based on exonuclease III and hybrid chain reaction dual signal amplification

At present, carcinoembryonic antigen (CEA) is considered a broad-spectrum cancer biomarker, and its accurate analysis in clinical samples can assist early cancer diagnosis and treatment. Herein, a novel electrochemical aptasensor has been proposed for CEA detection based on exonuclease III and hybrid chain reaction. The target CEA specifically binds to the aptamer region in hairpin probe 1 (defined as H1) by strong attraction, which leads the rest of the H1 triggering catalytic hairpin assembly to form a high quantity of H1 and hairpin probe 2 (defined as H2) double chain complex (denoted as H1@H2). Subsequently, the exonuclease III digests the complex of H1@H2 and liberates H1 to induce the first signal amplification. Simultaneously, a large number of generated trigger chains initiate a hybrid chain reaction and produce a second signal amplification. This proposed sensor exhibited excellent analytical performance for the detection of CEA, with wide linear range from 10 pg.mL-1 to 100 ng.mL-1 and low limit of detection of 0.84 pg.mL-1. Additionally, the biosensing strategy was successfully verified for direct measurement of CEA in human serum. Therefore, this elaborated sensor provides a new simple method for detecting CEA and exhibits great promise in the early screening of cancer.

Graphene-Assisted Electrochemical Sensor for Detection of Pancreatic Cancer Markers

Pancreatic cancer is a highly lethal gastrointestinal malignancy. Most patients are already in the middle to advanced stages of pancreatic cancer at the time of diagnosis and cannot be treated completely. As a single-atom planar two-dimensional crystal, graphene's unusual electronic structure, specific electronic properties and excellent electron transport capacity make it uniquely advantageous in the field of electrochemical sensing. In this mini-review, we summarize the potential application of graphene in pancreatic cancer detection. K-Ras gene, CEA and MicroRNA are important in the early diagnosis of pancreatic cancer.

Electrochemical Immunosensors with PQQ-Decorated Carbon Nanotubes as Signal Labels for Electrocatalytic Oxidation of Tris(2-carboxyethyl)phosphine

Nanocatalysts are a promising alternative to natural enzymes as the signal labels of electrochemical biosensors. However, the surface modification of nanocatalysts and sensor electrodes with recognition elements and blockers may form a barrier to direct electron transfer, thus limiting the application of nanocatalysts in electrochemical immunoassays. Electron mediators can accelerate the electron transfer between nanocatalysts and electrodes. Nevertheless, it is hard to simultaneously achieve fast electron exchange between nanocatalysts and redox mediators as well as substrates. This work presents a scheme for the design of electrochemical immunosensors with nanocatalysts as signal labels, in which pyrroloquinoline quinone (PQQ) is the redox-active center of the nanocatalyst. PQQ was decorated on the surface of carbon nanotubes to catalyze the electrochemical oxidation of tris(2-carboxyethyl)phosphine (TCEP) with ferrocenylmethanol (FcM) as the electron mediator. With prostate-specific antigen (PSA) as the model analyte, the detection limit of the sandwich-type immunosensor was found to be 5 pg/mL. The keys to success for this scheme are the slow chemical reaction between TCEP and ferricinum ions, and the high turnover frequency between ferricinum ions, PQQ. and TCEP. This work should be valuable for designing of novel nanolabels and nanocatalytic schemes for electrochemical biosensors.

Electrochemical and Electrochemiluminescence Dendrimer-based Nanostructured Immunosensors for Tumor Marker Detection: A Review

The usage of dendrimers or cascade molecules in the biomedical area has recently attracted much attention worldwide. Furthermore, dendrimers are interesting in clinical and pre-clinical applications due to their unique characteristics. Cancer is one of the most widespread challenges and important diseases, which has the highest mortality rate. In this review, the recent advances and developments (from 2009 up to 2019) in the field of electrochemical and electroluminescence immunosensors for detection of the cancer markers are presented. Moreover, this review covers the basic fabrication principles and types of electrochemical and electrochemiluminescence dendrimer-based immunosensors. In this review, we have categorized the current dendrimer based-electrochemical/ electroluminescence immunosensors into five groups: dendrimer/ magnetic particles, dendrimer/ferrocene, dendrimer/metal nanoparticles, thiol-containing dendrimer, and dendrimer/quantum dots based-immunosensors.

Construction of electrochemical immunosensors based on redox hydrogels for ultrasensitive detection of carcinoembryonic antigens

The introduction of cellulose nanocrystals (CNCs) endows a redox hydrogel with a larger specific surface area and better adhesion to an electrode.

A robust composite hydrogel consisting of polypyrrole and β-cyclodextrin-based supramolecular complex for the label-free amperometric immunodetection of motilin with well-defined dual signal response and high sensitivity

The label-free amperometric immunosensor is a simple, convenient and reliable method for the detection of diseases markers. Its performance heavily relies on the properties of the sensing substrate. In this paper, we proposed a robust composite hydrogel that consists of polypyrrole and vinyl ferrocene/mono-aldehyde β-cyclodextrin (β-CD) complex as a sensing and immobilizing substrate. Surprisingly, it was observed that the microstructure of the hybrid hydrogel could be well regulated by the feed ratio of vinylferrocene and so are the electrochemical properties. Depending on the dual electrochemical active compositions, a large loading capacity of antibodies and meanwhile the excellent conductivity, the square wave voltammetry results of the optimized immunosensor for the detection of motilin exhibited a well-defined dual signal response, with a wide linear range both from 10 pg mL-1 to 100 ng mL-1 for motilin, and an ultralow limit of detection of 6.29 pg mL-1 and 2.73 pg mL-1. More importantly, the immunosensor exhibited an especially sensitive response with the slope value as high as 31.342 and 25.751 respectively, which makes great sense in the practical diagnosis.

Stimulus-responsive surface-enhanced Raman scattering: a "Trojan horse" strategy for precision molecular diagnosis of cancer

Molecular diagnosis has played an increasingly important role in cancer detection. However, it remains challenging to develop an in situ analytical method capable of profiling the molecular phenotype of tumors for precision cancer diagnosis. A "Trojan horse" strategy based on stimulus-responsive surface-enhanced Raman scattering (SR-SERS) is reported here for selectively recording the comprehensive molecular information of tumors in situ, without resorting to destructive sample preparation and complex data analysis. This technique is employed to delineate the margin between tumors and normal tissues with high accuracy, and to further discriminate the molecular fingerprints of tumors in the early and late stages. Based on molecular profiling, we discovered that the signal ratios of fatty acid-to-phenylalanine could serve as promising indicators for identifying the primary tumors in different stages. This simple SR-SERS technique also provides a potential useful means for identifying tumor classifications or distinguishing primary and metastatic tumors.

An ultrasensitive immunosensor based on manganese dioxide-graphene nanoplatelets and core shell Fe3O4@Au nanoparticles for label-free detection of carcinoembryonic antigen

A novel electrochemical immunosensor was developed for label-free detection of carcinoembryonic antigen (CEA) as a cancer biomarker. The designed immunosensor was based on CEA antibody (anti-CEA) anchored with core shell Fe₃O₄@Au nanoparticles which were immobilized on a screen-printed carbon electrode modified with manganese dioxide decorating on graphene nanoplatelets (SPCE/GNP-MnO₂/Fe₃O₄@Au-antiCEA). The SPCE was placed onto a home-made electrode holder for easy handling. The approach was based on direct binding of CEA to a fixed amount of anti-CEA on the modified electrode for the specific detection using linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) monitored in a solution containing 5 mM [Fe(CN)₆^3-/4-] prepared in 0.1 M phosphate buffer at pH 7.4. The difference in signal response owing to the redox reaction of [Fe(CN)₆]^3-/4- before and after interaction with CEA was regarded as the immunosensor response corresponding directly to the CEA concentration. Under optimized conditions, the linear range of 0.001-100 ng/mL, and the detection limits of 0.10 pg/mL (LSV) and 0.30 pg/mL (EIS) were evaluated. The applicability of the immunosensor was verified by well-corresponding determination of CEA in diluted human serum samples by electrochemiluminescence (ECL) immunoassay. Therefore, the proposed immunosensor could be suitable enough for a real sample analysis of CEA.

Electrochemical biosensors for the detection of lung cancer biomarkers: A review

Cancer is one of the most widespread challenges and important diseases, which has the highest mortality rate. Lung cancer is the most common type of cancer, so that about 25% of all cancer deaths are related to the lung cancer. The lung cancer is classified as two different types with different treatment methodology: the small cell lung carcinoma and nonsmall cell lung carcinoma are two categories of the lung cancer. Since the lung cancer is often in the latent period in its early stages, therefore, early diagnosis of lung cancer has many challenges. Hence, there is a need for sensitive and reliable tools for preclinical diagnosis of lung cancer. Therefore, many detection methods have been employed for early detection of lung cancer. As lung cancer tumors growth in the body, the cancerous cells release numerous DNA, proteins, and metabolites as special biomarkers of the lung cancer. The levels of these biomarkers show the stages of the lung cancer. Therefore, detection of the biomarkers can be used for screening and clinical diagnosis of the lung cancer. There are numerous biomarkers for the lung cancer such as EGFR, CEA, CYFRA 21-1, ENO1, NSE, CA 19-9, CA 125 and VEGF. Nowadays, electrochemical methods are very attractive and useful in the lung cancer detections. So, in this paper, the recent advances and improvements (2010-2018) in the electrochemical detection of the lung cancer biomarkers have been reviewed.

Exonuclease III-assisted fluorometric aptasensor for the carcinoembryonic antigen using graphene oxide and 2-aminopurine

A reliable fluorometric assay is described for the determination carcinoembryonic antigen (CEA) using exonuclease III (Exo III) and a 2-aminopurine binding aptamer. In the absence of CEA, dsDNA is degraded by Exo III, and free 2-AP (which has a blue fluorescence with excitation/emission maxima of 310/365 nm) is released. Strong fluorescence is generated after addition of graphene oxide (GO) to the solution. However, the 2-AP modified DNA (T2) cannot be degraded in the presence of CEA by Exo III due to the interaction between CEA and aptamer T1. Hence, only weak fluorescence can be detected after addition of GO. In this system, CEA can be quantified in the 0.05 - 2 ng·mL^-1 concentration range with a detection limit of 30 pg·mL^-1 (at S/N = 3). The method was successfully applied to analyze serum samples for CEA. Graphical Abstract An exonuclease III-assisted fluorometric aptasensor has been developed for the detection of carcinoembryonic antigen using graphene oxide and 2-aminopurine.

Soft and flexible material-based affinity sensors

Recent advances in biosensors and point-of-care (PoC) devices are poised to change and expand the delivery of diagnostics from conventional lateral-flow assays and test strips that dominate the market currently, to newly emerging wearable and implantable devices that can provide continuous monitoring. Soft and flexible materials are playing a key role in propelling these trends towards real-time and remote health monitoring. Affinity biosensors have the capability to provide for diagnosis and monitoring of cancerous, cardiovascular, infectious and genetic diseases by the detection of biomarkers using affinity interactions. This review tracks the evolution of affinity sensors from conventional lateral-flow test strips to wearable/implantable devices enabled by soft and flexible materials. Initially, we highlight conventional affinity sensors exploiting membrane and paper materials which have been so successfully applied in point-of-care tests, such as lateral-flow immunoassay strips and emerging microfluidic paper-based devices. We then turn our attention to the multifarious polymer designs that provide both the base materials for sensor designs, such as PDMS, and more advanced functionalised materials that are capable of both recognition and transduction, such as conducting and molecularly imprinted polymers. The subsequent content discusses wearable soft and flexible material-based affinity sensors, classified as flexible and skin-mountable, textile materials-based and contact lens-based affinity sensors. In the final sections, we explore the possibilities for implantable/injectable soft and flexible material-based affinity sensors, including hydrogels, microencapsulated sensors and optical fibers. This area is truly a work in progress and we trust that this review will help pull together the many technological streams that are contributing to the field.

A Novel Carbon Quantum Dots Signal Amplification Strategy Coupled with Sandwich Electrochemiluminescence Immunosensor for the Detection of CA15-3 in Human Serum

A sensitive sandwich electrochemiluminescence immunosensor was established by employing graphene oxide-PEI-carbon quantum dots (CQDs)-Au nanohybrid as probe to measure carbohydrate antigen 15-3 (CA15-3), a breast cancer biomarker. In this work, nanocomposites of Ag nanoparticles and polydopamine (AgNPs-PDA) were synthesized by redox reaction between dopamine and Ag⁺. The nanocomposite with high surface area can provide an efficient substrate for immobilizing initial antibody (Ab1). Carbon quantum dots (CQDs) are fixed on polyethylenimine-functionalized graphene oxide (PEI-GO) by amide bonds. Au nanoparticles are modified on CQDs-decorated PEI-GO substrates. The secondary antibody (Ab2) was immobilized by AuNPs/CQDs-PEI-GO composite. CQDs can be assembled onto the surface of an electrode by incorporation of CA15-3 with Ab1 and Ab2. Under the synergistic action of AgNPs, polydopamine, AuNPs, and PEI-GO, the ECL signal of CQDs is greatly amplified as an excellent conductive material to facilitate electron transfer rate and further increase electrochemical detection capability. Under optimal conditions, the fabricated immunosensor showed a linear concentration range from 0.005 to 500 U mL^-1, with a detection limit of 0.0017 U mL^-1 (signal-to-noise ratio of 3) for CA15-3. The designed ECL immunosensor displayed receivable accuracy, excellent stability, and high specificity. The results of the detection of human serum samples are satisfactory, revealing that the method offers a potential application for the clinical diagnosis of tumor markers.

Ca2+-Triggered pH-Response Sodium Alginate Hydrogel Precipitation for Amplified Sandwich-Type Impedimetric Immunosensor of Tumor Marker

Signal amplification is of great significance in the ultrasensitive electrochemical impedimetric immunoassays for tumor marker detection. A cascaded signal amplification approach was designed using gold nanoparticle-CaCO₃ microspheres (AuNP-CaCO₃) to trigger pH-responsive alginate hydrogel precipitation for sandwich-type impedimetric immunosensor. AuNP-CaCO₃ exerts a large hindrance effect and can release Ca²⁺ ions under weak acidic conditions, and thus can serve as a multifunctional label. The hindrance effect of AuNP-CaCO₃ can significantly enhance the impedance response as the initial signal amplification. Then, part of CaCO₃ dissolves under weak acid conditions and releases Ca²⁺, which can cross-link with alginate to generate an insoluble alginate hydrogel precipitate on the sensing interface, significantly increasing the impedance signal. The impedance signal can be further amplified by making the hydrogel negatively charged based on the pH-responsive surface charge properties of the alginate hydrogel. Benefiting from the cascaded signal amplification, this impedimetric immunosensor exhibits a linear range from 1.0 fg mL^-1 to 100 ng mL^-1, an detection limit of 0.09 fg mL^-1, and ultrahigh sensitivity of 973.01 Ω (lg(ng mL^-1))^-1 toward the assay of prostate specific antigen (PSA).

3D biosensors in advanced medical diagnostics of high mortality diseases

Cardiovascular diseases, cancer, and diabetes are high mortality diseases, which account for almost two thirds of all deaths worldwide. Their early detection and continuous evaluation are fundamental for an improved patient prognosis and reduced socioeconomic impact. Current biosensor technologies are typically based on the analysis of whole blood samples from patients for the detection of disease-specific biomarkers. However, these technologies display serious shortcomings, such as reduced sensitivity and dynamic range, limited in vivo applicability, and lack of continuous monitoring. There is the urgent need for new diagnostic and treatment follow-up tools, which allow for the early detection of the pathology as well as for the continuous monitoring of the physiological responses to specific therapies. During the last years, a new generation of biosensor technologies with improved performance has emerged in the biomedical sector. The combination of advanced biomaterial methods, biochemical tools, and micro/nanotechnology approaches has resulted in the development of innovative three-dimensional (3D) biosensor platforms for advanced medical diagnosis. In this review, we report the most recent advances in the field of 3D biosensors for clinical applications, focusing on the diagnosis and monitoring of cardiovascular diseases, cancer, and diabetes. We discuss about their clinical performance compared to standard biosensor technologies, their implantable capability, and their integration into microfluidic devices to develop clinically-relevant models. Overall, we anticipate that 3D biosensors will drive us toward a new paradigm in medical diagnosis, resulting in real-time in vivo biosensors capable to significantly improve patient prognosis.

Voltammetric immunoassay of human IgG based on the release of cadmium(II) from CdS nanocrystals deposited on mesoporous silica nanospheres

The authors describe a nanocomposite that was obtained by in-situ deposition of CdS nanocrystals on mesoporous silica nanospheres (MSNs), and its use in an electrochemical immunoassay of human immunoglobulin G (HIgG). The MCN/CdS nanocomposite was covalently modified with the antibodies against HIgG and then employed in a voltammetric immunoassay at antibody-functionalized magnetic beads. Through sandwich immunoreaction, the MCN/CdS nanoprobes are quantitatively captured onto the magnetic beads where numerous Cd(II) ions are released in an acidic solution. The Cd(II) can be detected by anodic stripping voltammetry at a typical working potential of -0.78 V (vs. Ag/AgCl). In combination with the high loading of CdS on MSNs, the use of the stripping voltammetric analysis renders the method high sensitivity. A wide linear range varying from 0.01 to 100 ng mL^-1 is obtained for HIgG detection with a lower detection limit at 2.9 pg mL^-1. In addition, the preparation of the nanoprobe is inexpensive. The magnetic bead-based assay does not require complex manipulations. Therefore, this method is deemed to possess a wide scope in that it may be applied to other immunoassays. Graphical abstract Graphical Abstract contains poor quality and small text inside the artwork. Please do not re-use the file that we have rejected or attempt to increase its resolution and re-save. It is originally poor, therefore, increasing the resolution will not solve the quality problem. We suggest that you provide us the original format. We prefer replacement figures containing vector/editable objects rather than embedded images. Preferred file formats are eps, ai, tiff and pdf.A TIFF file at 900 dpi resolution of the Graphical Abstract has been attached via this online system. Schematic presentation of the preparation of the mesoporous silica nanosphere (MSN)/CdS nanocomposite for the electrochemical immunoassay of human IgG at magnetic beads. The high decoration of CdS on MSN and the stripping voltammetric analysis of Cd(II) ions render the method high sensitivity.

Microwave-assisted facile synthesis of poly(luminol-co-phenylenediamine) copolymers and their potential application in biomedical imaging

Conjugated copolymers have attracted much attention because of their outstanding photo-physical properties. The present work reports for the first time, microwave-assisted copolymerization of o-phenylenediamine with luminol using different weight ratios of the two monomers. The composition of the copolymers was confirmed by Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (¹H-NMR) while monomer reactivity ratios were determined using the Fineman–Ross method. Ultraviolet-visible spectroscopy revealed the variation in polaronic states upon copolymerization while X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses showed the morphology of the copolymers to be intermediate between that of the homopolymers. Confocal analysis and fluorescence studies revealed that the copolymers showed composition based blue as well as red emission which could be utilized for in vivo imaging of cancer cells.

Development of bioimaging agents based on poly(o-phenylendiamine and luminol).

Fundamentals and commercial aspects of nanobiosensors in point-of-care clinical diagnostics

Among various problems faced by mankind, health-related concerns are prevailing since long which are commonly found in the form of infectious diseases and different metabolic disorders. The clinical cure and management of such abnormalities are greatly dependent on the availability of their diagnoses. The conventional diagnostics used for such purposes are extremely powerful; however, most of these are limited by time-consuming protocols and require higher volume of test sample, etc. A new evolving technology called "biosensor" in this context shows an enormous potential for an alternative diagnostic device, which constantly compliments the conventional diagnoses. In this review, we have summarized different kinds of biosensors and their fundamental understanding with various state-of-the-art examples. A critical examination of different types of biosensing mechanisms is also reported highlighting the advantages of electrochemical biosensors for its great potentials in next-generation commercially viable modules. In recent years, a number of nanomaterials are extensively used to enhance not only the performance of biosensing mechanism, but also obtain robust, cheap, and fabrication-friendly durable mechanism. Herein, we have summarized the importance of nanomaterials in biosensing mechanism, their syntheses as well as characterization techniques. Subsequently, we have discussed the probe fabrication processes along with various techniques for assessing its analytical performances and potentials for commercial viability.

A palladium-platinum bimetal nanodendritic melamine network for signal amplification in voltammetric sensing of DNA

A sandwich-type electrochemical DNA sensor is described for the detection of oligonucleotides typical for MECP2 gene mutations. Palladium nanoparticles (PdNPs) and platinum nanoparticles (PtNPs) were used to synthesize flower-like PdPt nanodendrites (NDs) by a one-pot method. The PdPt NDs possess a high specific surface area and excellent catalytic capabilities. They served as the carrier for the signal DNA probe (SP) and simultaneously catalyze the reduction of hydrogen peroxide (H₂O₂). The PdPt NDs were modified with melamine, and this results in the formation of a PdPt-melamine network through stable interactions between the PdPt NDs and the three amino groups of each melamine molecule. The network exhibits excellent catalytic ability in enhancing the current signal response in the voltammetric detection of MECP2 gene mutation, best measured at -0.4 V vs. SCE and using H₂O₂ as the electrochemical probe. In addition, gold nanoflowers were electrodeposited on the electrode interface in order to accelerate electron transfer and to capture the capture probe. The sensor is stable and can detect MECP2 gene mutations in the 1 fmol·L^-1 to 1 nmol·L^-1 concentration range, with a 0.33 fmol·L^-1 lower detection limit at an S/N ratio of 3. Graphical abstract Schematic presentation of electrodes for the determination of the X-linked gene methyl-CpG-binding protein 2 (MECP2). The sensor is based on the electrooxidation of added H₂O₂ by using the melamine modified palladium platinum bimetal nanodendrites as network signal amplification strategy. This versatile platform expands studies on the detection of monogenic disease.

Nanomaterial-based biosensors for detection of prostate specific antigen

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