Efficiency of electrochemical immuno- vs. apta(geno)sensors for multiple cancer biomarkers detection

The interest in biosensors technology has been constantly growing over the last few years. It is still the biggest challenge to design biosensors able to detect two or more analytes in a single measurement. Electrochemical methods are frequently used for this purpose, mainly due to the possibility of applying two or more different redox labels characterized by independent and distinguished electrochemical signals. In addition to antibodies, nucleic acids (aptamers) have been increasingly used as bioreceptors in the construction of such sensors. Within this review paper, we have collected the examples of electrochemical immuno- and geno(apta)sensors for simultaneous detection of multiple analytes. Based on many published literature examples, we have emphasized the recent application of multiplexed platforms for detection of cancer biomarkers. It has allowed us to compare the progress in design strategies, including novel nanomaterials and amplification of signals, to get as low as possible limits of detection. We have focused on multi-electrode and multi-label strategies based on redox-active labels, such as ferrocene, anthraquinone, methylene blue, thionine, hemin and quantum dots, or metal ions such as Ag+, Pb2+, Cd2+, Zn2+, Cu2+ and others. We have finally discussed the possible way of development, challenges and prospects in the area of multianalyte electrochemical immuno- and geno(apta)sensors.

Synthetic Receptors for Early Detection and Treatment of Cancer

Over recent decades, synthetic macrocyclic compounds have attracted interest from the scientific community due to their ability to selectively and reversibly form complexes with a huge variety of guest moieties. These molecules have been studied within a wide range of sensing and other fields. Within this review, we will give an overview of the most common synthetic macrocyclic compounds including cyclodextrins, calixarenes, calixresorcinarenes, pillarenes and cucurbiturils. These species all display the ability to form a wide range of complexes. This makes these compounds suitable in the field of cancer detection since they can bind to either cancer cell surfaces or indeed to marker compounds for a wide variety of cancers. The formation of such complexes allows sensitive and selective detection and quantification of such guests. Many of these compounds also show potential for the detection and encapsulation of environmental carcinogens. Furthermore, many anti-cancer drugs, although effective in in vitro tests, are not suitable for use directly for cancer treatment due to low solubility, inherent instability in in vivo environments or an inability to be adsorbed by or transported to the required sites for treatment. The reversible encapsulation of these species in a macrocyclic compound can greatly improve their solubility, stability and transport to required sites where they can be released for maximum therapeutic effect. Within this review, we intend to present the use of these species both in cancer sensing and treatment. The various macrocyclic compound families will be described, along with brief descriptions of their synthesis and properties, with an outline of their use in cancer detection and usage as therapeutic agents. Their use in the sensing of environmental carcinogens as well as their potential utilisation in the clean-up of some of these species will also be discussed.

Facile preparation of Ru nanoassemblies for electrochemical immunoassay of carcinoembryonic antigen in clinical serum

Abnormal expression of carcinoembryonic antigen (CEA) can be used for early diagnosis of various cancers (e.g. colorectal cancer, cervical carcinomas, and breast cancer). In this work, using l-cysteine-ferrocene-Ruthenium nanocomposites (L-Cys-Fc-Ru) to immobilize secondary antibody (Ab₂) and Au nanoparticles (NPs) as the substrate to ensure accurate capture of primary antibody (Ab₁), a signal-on sandwich-like biosensor was constructed in the presence of CEA. Specifically, Ru nanoassemblies (NAs) were first prepared by a facile one-step solvothermal approach as signal amplifiers for the electrical signal of Fc. Based on specific immune recognition, as the increase of CEA concentration, the content of L-Cys-Fc-Ru-Ab₂ captured on the electrode surface also increased, thus the signal of Fc gradually increased. Therefore, the quantitative detection of CEA can be realized according to the peak current of Fc. After a series of experiments, it was found that the biosensor has a wide detection range from 1.0 pg mL^-1 to 100.0 ng mL^-1 and a low detection limit down to 0.5 pg mL^-1, as well as good selectivity, repeatability and stability. Furthermore, satisfactory results were also obtained for the determination of CEA in serums, which were comparable to commercial electrochemiluminescence (ECL) method. The developed biosensor shows great potential in clinical applications.

Paper-based multiplex biosensors for inexpensive healthcare diagnostics: a comprehensive review

Multiplex detection is a smart and an emerging approach in point-of-care testing as it reduces analysis time and testing cost by detecting multiple analytes or biomarkers simultaneously which are crucial for disease detection at an early stage. Application of inexpensive substrate such as paper has immense potential and matter of research interest in the area of point of care testing for multiplexed analysis as it possesses several unique advantages. This study presents the use of paper, strategies adopted to refine the design created on paper and lateral flow strips to enhance the signal, increase the sensitivity and specificity of multiplexed biosensors. An overview of different multiplexed detection studies performed using biological samples has also been reviewed along with the challenges and advantages offered by multiplexed analysis.

A sensitive electrochemiluminescence immunosensor for the detection of CA15-3 based on CeO2/Pt/rGO as a novel co-reaction accelerator

In this work, we successfully constructed a label-free electrochemiluminescence (ECL) immunosensor for the detection of breast cancer marker antigen (CA15-3). In particular, 3,4,9,10-perylenetetracarboxylic acid (PTCA) is cleverly attached to the surface of silica spheres as a luminophore (NH₂-SiO₂-PTCA), which greatly alleviates the disadvantage of PTCA anti-induced aggregated luminescence and improves the ECL performance. Furthermore, Pt nanoparticles were used to dope CeO₂ and introducing reduced graphene oxide (rGO) to prepare CeO₂/Pt/rGO composites as a novel co-reaction accelerator. Among them, Pt nanoparticles were used to improve the electrical conductivity of CeO₂, and the use of rGO as a substrate allows for a more uniform dispersion of CeO₂ to increase the catalytic surface area, which effectively improves the performance of the co-reaction accelerator and thus increasing the ECL intensity of the PTCA/S₂O₈^2- system. Under the optimal conditions, the designed ECL immunosensor showed satisfactory results in the determination of CA15-3 with a linear range of 12.00 mU mL^-1 - 120.00 U mL^-1 and a low detection limit of 1.348 mU mL^-1. Importantly, the resulting biosensor has good stability, high sensitivity and reliable reproducibility, suggesting its potential application in clinical research.

Ultrasensitive Detection of Carcinoembryonic Antigen by Chitosan/Polythiophene/CdTe Electrochemical Biosensor

A facile method for the in situ fabrication of chitosan/polythiophene/CdTe (CS/PTh/CdTe) nanocomposite has been developed. It was then connected with anti-CEA (Ab), which was evoked for the electrochemical detection of carcinoembryonic antigen (CEA, Ag) within K₄Fe(CN)₆. The results indicate that CS/PTh/CdTe/GCE has a high selectivity for the detection of CEA with a wide linear range of 0.0001-10000 ng/mL and excellent sensitivity with a low detection limit of 40 fg/mL. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), X-ray photoelectron spectroscopy (XPS), and in situ FT-IR spectra are evoked to study the mechanism of detection of CEA via CS/PTh/CdTe/GCE. The high sensitivity of the electrochemical sensor is due to the fact that the electrochemical oxidation products of K₄Fe(CN)₆ can directly oxidize CdTe from a low energy state to a high energy state (CdTe)*, making CdTe more prone to be oxidized and facilitate electron transfer. The developed electrochemical biosensor can be used for the detection of real samples, providing a precise method for the detection of CEA with potential application in the clinical detection of tumors.

In situ growth of WO3/BiVO4 nanoflowers onto cellulose fibers to construct photoelectrochemical/colorimetric lab-on-paper devices for the ultrasensitive detection of AFP

In this work, novel dual-mode lab-on-paper devices based on in situ grown WO₃/BiVO₄ heterojunctions onto cellulose fibers, as signal amplification probes, were successfully fabricated by the integration of photoelectrochemical (PEC)/colorimetric analysis technologies into a paper sensing platform for the ultrasensitive detection of alpha-fetoprotein (AFP). Specifically, to achieve an impressive PEC performance of the lab-on-paper device, the WO₃/BiVO₄ heterojunction was in situ grown onto the surface of cellulose fibers assisted with Au nanoparticle (Au NP) functionalization for enhancing the conductivity of the working zone of the device. With the target concentration increased, more immune conjugates could be captured by the proposed paper photoelectrode, which could lead to a quantitative decrease in the photocurrent intensity, eventually realizing the accurate PEC signal readout. To meet the requirement of end-user application, a colorimetric signal readout system was designed for the lab-on-paper device based on the color reaction of 3,3'5,5'-tetramethylbenzidine (TMB) oxidized by WO₃/BiVO₄ nanoflowers in the presence of H₂O₂. Noticeably, it is the first time that the WO₃/BiVO₄ heterojunction is in situ grown onto cellulose fibers, which enhances the sensitivity in view of both their PEC activity and catalytic ability. By controlling the conversion process of hydrophobicity and hydrophilicity on the lab-on-paper device combined with diverse origami methods, the dual-mode PEC/colorimetric signal output for the ultrasensitive AFP detection was realized. Under optimal conditions, the proposed dual-mode lab-on-paper device could enable the sensitive PEC/colorimetric diagnosis of AFP in the linear range of 0.09-100 ng mL^-1 and 5-100 ng mL^-1 with the limit of detection of 0.03 and 1.47 ng mL^-1, respectively.

A label-free multiplex electrochemical biosensor for the detection of three breast cancer biomarker proteins employing dye/metal ion-loaded and antibody-conjugated polyethyleneimine-gold nanoparticles

A new electrochemical immunosensor is developed for the label-free simultaneous detection of mucin1 (MUC1), cancer antigen 15-3 (CA15-3), and human epidermal growth factor receptor 2 (HER2) early breast cancer biomarkers. The biosensor is simply designed using the deposition of three different systems of redox species-antibody-conjugated polyethylenimine coated-gold nanoparticles (PEI-AuNPs), for the first time. The screen-printed carbon electrode (SPCE) comprising a three-working electrode array is modified with the conjugated PEI-AuNPs. Multiplex sensing is performed by utilizing the distinguishable electrochemical responses of the redox-active species; anthraquinone-2-carboxylic acid (AQ), thionine chloride (TH), and AgNO3 (Ag+) on the PEI-AuNPs conjugates for the detection of MUC1, CA15-3, and HER2, respectively. The single-run determination of the biomarkers by the proposed immunosensor is carried out by measuring the decrease (%) in the oxidation peak currents due to the formation of three kinds of antibody-antigen complexes. The decreased currents are logarithmically proportional to the antigen concentrations in the ranges of 0.10-100 U mL-1 CA15-3 and 0.10-100 ng mL-1 MUC1 and HER2 with detection limits of 0.21 U mL-1, 0.53 ng mL-1 and 0.50 ng mL-1, respectively, which are significantly lower than the clinically relevant cut-off levels. The sensor reveals high selectivity and satisfactory reproducibility. After storing for two weeks, the sensor retains the responses with ca. 90% of the initial currents. The immunosensor is successfully applied to detect three tumor markers in human serum and can provide a new technological platform for the development of low-cost, highly stable, sensitive, selective, and point-of-care (POC) diagnosis.

Nanostructure-Based Electrochemical Immunosensors as Diagnostic Tools

Electrochemical immunosensors are affinity-based biosensors characterized by several useful features such as specificity, miniaturizability, low cost and simplicity, making them very interesting for many applications in several scientific fields. One of the significant issues in the design of electrochemical immunosensors is to increase the system’s sensitivity. Different strategies have been developed, one of the most common is the use of nanostructured materials as electrode materials, nanocarriers, electroactive or electrocatalytic nanotracers because of their abilities in signal amplification and biocompatibility. In this review, we will consider some of the most used nanostructures employed in the development of electrochemical immunosensors (e.g., metallic nanoparticles, graphene, carbon nanotubes) and many other still uncommon nanomaterials. Furthermore, their diagnostic applications in the last decade will be discussed, referring to two relevant issues of present-day: the detection of tumor markers and viruses.

Multiplex bioassaying of cancer proteins and biomacromolecules: Nanotechnological, structural and technical perspectives

Since the specific proteins (carbohydrate antigens, ligands and interleukins) get raised up in body tissue or fluids in cancer cases, early detection of them will provide an effective treatment and survival rate. Sensitive and accurate determination of multiple cancer proteins can be engaged in chorus by simultaneous/multiplex detection in the biomedical fields. Bioassaying technology is one of the non-invasive, high-sensitive, and economical methods. Currently, extensive application of nanomaterial (biocompatible polymers, metallic and metal oxide) in bioassays resulted in ultra-high sensitive and selective diagnosis. This review article focuses on types of multiplex bioassays for delicate and specific determination of cancer proteins for diagnostic aims. It also covers two modes of multiplex bioassays as multi labeled bioassays and spatially-separated test zones (multi-electrode mode). In this review, the nanotechnological, structural, and technical perspectives in the multiplex analysis of cancer proteins were discussed. Finally, the use of different types of nanomaterials, polysaccharides, biopolymers and their advantages in signal amplification are discussed.

Graphene-based stochastic sensors for pattern recognition of gastric cancer biomarkers in biological fluids

This paper proposes pattern recognition of gastric cancer biomarkers CEA, CA19-9 and p53 in whole blood and urine samples using a stochastic sensor based on exfoliated graphene (E-NGr) paste modified with protoporphyrin IX. The proposed sensor covered large ranges of concentrations: 1 × 10[Formula: see text]–1 × 10[Formula: see text]g/mL for CEA, 1 × 10[Formula: see text]–1 × 102 U/mL for CA19-9, and 0.2–5.0 [Formula: see text]g/mL for p53. These ranges allowed the determination of the three biomarkers from early to latest stages of gastric cancer. Validation of the pattern recognition of gastric cancer biomarkers was accomplished using biological samples: whole blood and urine.

Sandwich-type electrochemical immunosensor for carcinoembryonic antigen detection based on the cooperation of a gold-vertical graphene electrode and gold@silica-methylene blue

In this study, a sandwich-type electrochemical (EC) immunosensor was proposed to detect a carcinoembryonic antigen (CEA) based on Au-graphene and Au@SiO₂-methylene blue (MB). The Au nanoparticles (NPs)-vertical graphene (VG) electrode efficiently amplifies the response signal by immobilizing a large amount of the coating antibody (Ab) and is characterized by excellent electrocatalytic activity. The MB nanodot-loaded Au@SiO₂ carriers with core-shell nanostructure and detection Ab were used to construct the Ab-Au@SiO₂-MB label, which improved the sensitivity due to the high EC signal of MB nanodots and the high labeling effect between the detection Ab and MB probe. A novel double-Ab sandwich strategy was developed to further improve the sensitivity and stability based on the same specificity of the coating and detection Abs for the recognition of CEA. Under optimal conditions, the developed EC sensor exhibited a wide linear range from 1 fg mL^-1 to 100 ng mL^-1, with an ultralow detection limit of 0.8 fg mL^-1 (S/N = 3). The feasibility in the clinical application of the EC sensor was verified by the in vitro detection of CEA in human serum.

Improving the anti-fouling property and permeate flux of hollow fiber composite nanofiltration membrane using β-cyclodextrin

Hollow fiber composite NF membranes with improved anti-fouling property and water flux were prepared via interfacial polymerizationand layer-by-layer method using polyethylenimine (PEI), isophthaloyl dichloride (IPC), and β-cyclodextrin (β-CD). The chemical structures and the morphologies of the resultant NF membranes were characterized by attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy and scanning electron microscopy (SEM). The effects of β-CD concentration on membrane morphologies, nanofiltration performances, surface hydrophilicities and anti-fouling properties were investigated. It was found that the permeate flux increased with increasing the β-CD concentration, and no decline of rejection was observed. The results showed that the introduction of β-CD improved surface hydrophilicities and anti-fouling performances of composite hollow fiber NF membranes. The water contact angles decreased from 61.3° to 23° within creasing the concentration of β-CD from 0 to 2.0 wt.%. The resultant hollow fiber composite NF membrane showed an excellent anti-fouling property with the flux recovery ratio of 97.6%, which was much better than that of the original polyamide (PA) NF membranes.

Nanostructures for nonlabeled and labeled electrochemical immunosensors: Simultaneous electrochemical detection of cancer markers: A review

The simultaneous electrochemical determination of multiple tumor antigens has attracted a great deal of attention, which can effectively enhance the capability and accuracy of the analysis. Nanostructured materials mostly played a key major role in the electrochemical immunosensors fabrication and operation improvement. This review focused mainly on the protocols for using nanostructures to fabricate electrochemical (nonlabeled@label-free and labeled@sandwich-type) immunosensors. Furthermore, this review has also described the diverse classes of electroactive nanospecies which are a complementary part of any immunosensor that assists to reach the selectivity for the target antigen. Finally, the important analytical characteristics of the published immunosensors were discussed (electrochemical detection technique, linear range, and detection limit). Studies published between the years 2009-2018 have been included in this review.

Advances in electrochemical immunosensors

Immunosensors are compact tools on which antibody and antigen interactions are formed. The specific interaction between antibody and antigen is detected by using a transducer and an electrical signal is measured. This specific interaction between these molecules makes immunosensor very attractive for several applications in different fields. Electrochemical immunosensors are successful devices in selective and sensitive detection of several analytes. Electrochemical transducing methods such as voltammetric, potentiometric, conductometric or impedimetric have been utilized in different applications due to their excellent properties such as being low-cost, sensitivity and simplicity. In this chapter, the fundamentals of electrochemical immunosensors are summarized and different applications in food, environmental and clinical analyses are investigated and discussed.

Collision of Aptamer/Pt Nanoparticles Enables Label-Free Amperometric Detection of Protein in Rat Brain

Single particle collision is emerging as a powerful and sensitive technique for analyzing small molecules, however, its application in biomacromolecules detection, for example, protein, in complex biological environments is still challenging. Here, we present the first demonstration on the single particle collision that can be developed for the detection of platelet-derived growth factor (PDGF), an important protein involved in the central nervous system in living rat brain. The system features Pt nanoparticles (PtNPs) conjugated with the PDGF recognition aptamer, suppressing the electrocatalytic collision of PtNPs toward the oxidation of hydrazine. In the presence of PDGF, the stronger binding between targeted protein and the aptamer disrupts the aptamer/PtNPs conjugates, recovering the electrocatalytic performance of PtNPs, and allowing quantitative, selective, and highly sensitive detection of PDGF in cerebrospinal fluid of rat brain.

A review on graphene-based nanocomposites for electrochemical and fluorescent biosensors

Biosensors with high sensitivity, selectivity and a low limit of detection, reaching nano/picomolar concentrations of biomolecules, are important to the medical sciences and healthcare industry for evaluating physiological and metabolic parameters.

Ultrasensitive sandwich-type immunosensor for cardiac troponin I based on enhanced electrocatalytic reduction of H2O2 using β-cyclodextrins functionalized 3D porous graphene-supported Pd@Au nanocubes

A signal amplification principle based on increased electrocatalytic reduction of H₂O₂ by the CDs-3D-PG-Pd@Au NCs using the mediated effect of Th.

Biochemical sensing with macrocyclic receptors

Preventive healthcare asks for the development of cheap, precise and non-invasive sensor devices for the early detection of diseases and continuous population screening. The actual techniques used for diagnosis, e.g. MRI and PET, or for biochemical marker sensing, e.g. immunoassays, are not suitable for continuous monitoring since they are expensive and prone to false positive responses. Synthetic supramolecular receptors offer new opportunities for the creation of specific, selective and cheap sensor devices for biological sensing of specific target molecules in complex mixtures of organic substances. The fundamental challenges faced in developing such devices are the precise transfer of the molecular recognition events at the solid-liquid interface and its transduction into a readable signal. In this review we present the progress made so far in turning synthetic macrocyclic hosts, namely cyclodextrins, calixarenes, cucurbiturils and cavitands, into effective biochemical sensors and the strategies utilized to solve the above mentioned issues. The performances of the developed sensing devices based on these receptors in detecting specific biological molecules, drugs and proteins are critically discussed.

A single-interface photoelectrochemical sensor based on branched TiO2 nanorods@strontium titanate for the detection of two biomarkers

Based on the enhanced photogenerated charge-separation properties of B-TiO₂ NRs@SrTiO₃ heterostructures, a photoelectrochemical sensor for detecting alpha fetoprotein and cancer antigen 153 at a single interface was first established.

Graphene- gold based nanocomposites applications in cancer diseases; Efficient detection and therapeutic tools

Early detection and efficient treatment of cancer disease remains a drastic challenge in 21st century. Throughout the bulk of funds, studies, and current therapeutics, cancer seems to aggressively advance with drug resistance strains and recurrence rates. Nevertheless, nanotechnologies have indeed given hope to be the next generation for oncology applications. According to US National cancer institute, it is anticipated to revolutionize the perspectives of cancer diagnosis and therapy. With such success, nano-hybrid strategy creates a marvelous preference. Herein, graphene-gold based composites are being increasingly studied in the field of oncology, for their outstanding performance as robust vehicle of therapeutic agents, built-in optical diagnostic features, and functionality as theranostic system. Additional modes of treatments are also applicable including photothermal, photodynamic, as well as combined therapy. This review aims to demonstrate the various cancer-related applications of graphene-gold based hybrids in terms of detection and therapy, highlighting the major attributes that led to designate such system as a promising ally in the war against cancer.

A highly sensitive electrochemical immunosensor for hepatitis B virus surface antigen detection based on Hemin/G-quadruplex horseradish peroxidase-mimicking DNAzyme-signal amplification

Here we prepared an electrochemical immunosensor employing Au sheet as working electrode, Fe₃O₄ magnetic nanoparticles (MNPs) as supporting matrix and hemin/G-quadruplex DNAzyme as signal amplifier for determination of hepatitis B virus surface antigen (HBsAg). First, the primary antibody of HBs (Ab₁) was immobilized on the surface of the carboxyl-modified MNPs. Then, the assembly of antibody and alkylthiol/G-quadruplex DNA/hemin on gold nanoparticles was used as bio-bar-coded nanoparticle probe. Protein target was sandwiched between the primary antibody of HBs (Ab₁) immobilized on the MNPs and hemin bio-bar-coded AuNPs probe labeled antibody (Ab₂). Hemin/G-quadruplex structure as HRP mimicking-DNAzyme significantly improved the catalytic reduction of H₂O₂ by oxidation of methylene blue (MB). Square wave voltammetry signals of MB provided quantitative measurements of HBsAg with a linear concentration range of 0.3-1000 pgmL^-1 and detection limit of 0.19 pgmL^-1. Due to efficient catalytic activity of HRP mimicking-DNAzyme, the proposed immunosensor exhibited high sensitivity and it holds great promise for clinical application and provides a new platform for immunosensor development and fast disease diagnosis.

A battle between spherical and cube-shaped Ag/AgCl nanoparticle modified imprinted polymer to achieve femtogram detection of alpha-feto protein

In this work, a sensitive and selective molecularly imprinted polymer modified electrochemical sensor was developed for the detection of the hepatocellular carcinoma (HCC) biomarker, alpha feto protein (AFP) on the surface of specifically designed Ag/AgCl nanoparticles. Herein, for the first time, the effect of the shape of nanoparticles on the behavior of an imprinted polymer was studied using cube- and spherical-shaped Ag/AgCl nanoparticles. It was found that cube-shaped nanoparticles have high surface to volume ratios and higher electrocatalytic activity, and are, therefore, a suitable platform for the synthesis of imprinted polymers. Herein, we have demonstrated how a change in the morphology of the nanomaterials can affect the electrochemical and adsorption properties of an imprinted polymer towards the target analyte (here, AFP). A cube-shaped nanoparticle@imprinted polymer was used for the fabrication of the electrochemical sensor, the analytical performance of which was shown, by a square wave stripping voltammetric technique, to be good for the detection of AFP. The current response of the electrochemical sensor was linear for AFP concentrations in the range from 0.10 to 700.0 pg mL-1, with an ultra trace detection limit of 24.6 fg mL-1. This sensor offers high selectivity, sensitivity, simplicity and clinical applicability for AFP determination in human blood serum, plasma, and urine, without using antibodies or any biological components, this has not been reported for previously reported systems. The proposed sensor has the potential to be used as an alternative to the commercially available, costly, sophisticated enzyme-linked immunosorbent assay kits for AFP determination.