Detection of Interferon gamma using graphene and aptamer based FET-like electrochemical biosensor

Amplified Detection of the Aptamer-Vanillin Complex with the Use of Bsm DNA Polymerase

The electrochemical detection of interactions between aptamers and low-molecular-weight targets often lacks sensitivity. Signal amplification improves the detection of the aptamer-analyte complex; Bsm DNA polymerase was used to amplify the signal from the interaction of vanillin and its aptamer named Van_74 on an ion-sensitive field-effect transistor (ISFET)-based biosensor. The aptamer was immobilized on the ISFET sensitive surface. A short DNA probe was hybridized with the aptamer and dissociated from it upon vanillin addition. A free probe interacted with a special DNA molecular beacon initiated the Bsm DNA polymerase reaction that was detected by ISFET. A buffer solution suitable for both aptamer action and Bsm DNA polymerase activity was determined. The ISFET was shown to detect the Bsm DNA polymerase reaction under the selected conditions. Vanillin at different concentrations (1 × 10-6-1 × 10-8 M) was detected using the biosensor with signal amplification. The developed detection system allowed for the determination of vanillin, starting at a 10-8 M concentration. Application of the Bsm DNA polymerase resulted in a 15.5 times lower LoD when compared to the biosensor without signal amplification (10.1007/s00604-017-2586-4).

Aptasensor based optical detection of glycated albumin for diabetes mellitus diagnosis

Glycated albumin (GA) has been reported as an important biomarker for diabetes mellitus. This study investigates an optical sensor comprised of deoxyribonucleic acid (DNA) aptamer, semiconductor quantum dot and gold (Au) nanoparticle for the detection of GA. The system functions as a 'turn on' sensor because an increase in photoluminescence intensity is observed upon the addition of GA to the sensor. This is possibly because of the structure of the DNA aptamer, which folds to form a large hairpin loop before the addition of the analyte and is assumed to open up after the addition of target to the sensor in order to bind to GA. This pushes the quantum dot and the Au nanoparticle away causing an increase in photoluminescence. A linear increase in photoluminescence intensity and quenching efficiency of the sensor is observed as the GA concentration is varied between 0-14 500 nM. Time based photoluminescence studies with the sensor show the decrease in binding rate of the aptamer to the target within a specific time period. The sensor was found to have a higher selectivity towards GA than other control proteins. Further investigation of this simple sensor with greater number of clinical samples can open up avenues for an efficient diagnosis and monitoring of diabetes mellitus when used in conjunction with the traditional method of glucose level monitoring.

Real-Time Monitoring of Insulin Using a Graphene Field-Effect Transistor Aptameric Nanosensor

This paper presents an approach to the real-time, label-free, specific, and sensitive monitoring of insulin using a graphene aptameric nanosensor. The nanosensor is configured as a field-effect transistor, whose graphene-based conducting channel is functionalized with a guanine-rich IGA3 aptamer. The negatively charged aptamer folds into a compact and stable antiparallel or parallel G-quadruplex conformation upon binding with insulin, resulting in a change in the carrier density, and hence the electrical conductance, of the graphene. The change in the electrical conductance is then measured to enable the real-time monitoring of insulin levels. Testing has shown that the nanosensor offers an estimated limit of detection down to 35 pM and is functional in Krebs-Ringer bicarbonate buffer, a standard pancreatic islet perfusion medium. These results demonstrate the potential utility of this approach in label-free monitoring of insulin and in timely prediction of accurate insulin dosage in clinical diagnostics.

Graphene oxide and DNA aptamer based sub-nanomolar potassium detecting optical nanosensor

Quantum-dot (QD) based nanosensors are frequently used by researchers to detect small molecules, ions and different biomolecules. In this article, we present a sensor complex/system comprised of deoxyribonucleic acid (DNA) aptamer, gold nanoparticle and semiconductor QD, attached to a graphene oxide (GO) flake for detection of potassium. As reported herein, it is demonstrated that QD-aptamer-quencher nanosensor functions even when tethered to GO, opening the way to future applications where sensing can be accomplished simultaneously with other previously demonstrated applications of GO such as serving as a nanocarrier for drug delivery. Herein, it is demonstrated that the DNA based thrombin binding aptamer used in this study undergoes the conformational change needed for sensing even when the nanosensor complex is anchored to the GO. Analysis with the Hill equation indicates the interaction between aptamer and potassium follows sigmoidal Hill kinetics. It is found that the quenching efficiency of the optical sensor is linear with the logarithm of concentration from 1 pM to 100 nM and decreases for higher concentration due to unavailability of aptamer binding sites. Such a simple and sensitive optical aptasensor with minimum detection capability of 1.96 pM for potassium ion can also be employed in-vitro detection of different physiological ions, pathogens and disease detection methods.

Novel Electrochemiluminescence-Sensing Platform for the Precise Analysis of Multiple Latent Tuberculosis Infection Markers

Latent tuberculosis infection (LTBI) is one of the major contributing factors for the high incidence of tuberculosis, and the low contents of LTBI markers in human serum present a great challenge for the diagnosis of LTBI. Here, we reported a novel electrochemiluminescence (ECL)-sensing platform for the precise analysis of multiple LTBI markers, interferon-gamma (IFN-γ) and interleukin (IL)-2. In this approach, self-prepared carbon quantum dots (CQDs) and luminol were integrated onto gold nanoparticles (AuNPs), which were further enriched on the surface of magnetic bead (MB) to create two solid-phase ECL nanoprobes (MB@Au@CQDs and MB@Au@luminol) for improving the detection sensitivity efficiently. Graphene oxide (GO) and AuNPs were electrodeposited onto a patterned indium tin oxide (ITO) electrode with two spatially resolved areas in sequence to form two sensitive and stable sensing areas. IFN-γ-antibody (Ab)₁ and IL-2-Ab₁ were separately immobilized on the two sensing areas to capture the corresponding LTBI markers, which were further recognized by IFN-γ-Ab₂ and IL-2-Ab₂ labeled as MB@Au@CQDs and MB@Au@luminol. The ECL intensity depended linearly on the content of IFN-γ and IL-2 in the range of 0.01-1000 pg mL^-1, with a low detection limit of 10 fg mL^-1. The proposed ECL-sensing platform is simple, sensitive, accurate, reliable, and specific to the detection of rare IFN-γ and IL-2 in human serum and provides a valuable protocol for facilitating fast and precise diagnosis of LTBI.

Electrochemical determination of M. tuberculosis antigen based on Poly(3,4-ethylenedioxythiophene) and functionalized carbon nanotubes hybrid platform

An electrochemical DNA aptasensor for the detection of Mycobacterium tuberculosis (M. tb) antigen MPT64, was developed using Poly(3,4-ethylenedioxythiophene) (PEDOT) doped with carbon nanotubes (CNTs). The biotinylated aptamer was immobilized onto streptavidin attached to -COOH functionalized CNTs via streptavidin-biotin interaction. Various characterization studies as FT-IR, FE-SEM, EIS and DPV were done to validate each fabrication step of the aptasensor. Optimization studies related to aptamer concentration and response time were performed. The electrochemical signal generated from the aptamer-target molecule interaction was monitored electrochemically by differential pulse voltammetry in the presence of [Fe(CN)₆]^3-/4- as a redox probe. The aptasensor exhibited limit of detection of 0.5±0.2fgmL^-1 within 15min with stability of 27 days at 4°C and reusability of 7 times after repeated regeneration with 50mM NaOH. The potential application of the aptasensor was established by spike-in studies to obtain recovery in between (88-95)%.

Rapid and Label-Free Detection of Interferon Gamma via an Electrochemical Aptasensor Comprising a Ternary Surface Monolayer on a Gold Interdigitated Electrode Array

A label-free electrochemical impedance spectroscopy (EIS) aptasensor for rapid detection (<35 min) of interferon-gamma (IFN-γ) was fabricated by immobilizing a RNA aptamer capture probe (ACP), selective to IFN-γ, on a gold interdigitated electrode array (Au IDE). The ACP was modified with a thiol group at the 5' terminal end and subsequently co-immobilized with 1,6-hexanedithiol (HDT) and 6-mercapto-1-hexanolphosphate (MCH) to the gold surface through thiol-gold interactions. This ACP/HDT-MCH ternary surface monolayer facilitates efficient hybridization with IFN-γ and displays high resistance to nonspecific adsorption of nontarget proteins [i.e., fetal bovine serum (FBS) and bovine serum albumin (BSA)]. The Au IDE functionalized with ACP/HDT-MCH was able to measure IFN-γ in actual FBS solution with a linear sensing range from 22.22 pM to 0.11 nM (1-5 ng/mL) and a detection limit of 11.56 pM. The ability to rapidly sense IFN-γ within this sensing range makes the developed electrochemical platform conducive toward in-field disease detection of a variety of diseases including paratuberculosis (i.e., Johne's Disease). Furthermore, experimental results were numerically validated with an equivalent circuit model that elucidated the effects of the sensing process and the influence of the immobilized ternary monolayer on signal output. This is the first time that ternary surface monolayers have been used to selectively capture/detect IFN-γ on Au IDEs.

Emerging Cytokine Biosensors with Optical Detection Modalities and Nanomaterial-Enabled Signal Enhancement

Protein biomarkers, especially cytokines, play a pivotal role in the diagnosis and treatment of a wide spectrum of diseases. Therefore, a critical need for advanced cytokine sensors has been rapidly growing and will continue to expand to promote clinical testing, new biomarker development, and disease studies. In particular, sensors employing transduction principles of various optical modalities have emerged as the most common means of detection. In typical cytokine assays which are based on the binding affinities between the analytes of cytokines and their specific antibodies, optical schemes represent the most widely used mechanisms, with some serving as the gold standard against which all existing and new sensors are benchmarked. With recent advancements in nanoscience and nanotechnology, many of the recently emerging technologies for cytokine detection exploit various forms of nanomaterials for improved sensing capabilities. Nanomaterials have been demonstrated to exhibit exceptional optical properties unique to their reduced dimensionality. Novel sensing approaches based on the newly identified properties of nanomaterials have shown drastically improved performances in both the qualitative and quantitative analyses of cytokines. This article brings together the fundamentals in the literature that are central to different optical modalities developed for cytokine detection. Recent advancements in the applications of novel technologies are also discussed in terms of those that enable highly sensitive and multiplexed cytokine quantification spanning a wide dynamic range. For each highlighted optical technique, its current detection capabilities as well as associated challenges are discussed. Lastly, an outlook for nanomaterial-based cytokine sensors is provided from the perspective of optimizing the technologies for sensitivity and multiplexity as well as promoting widespread adaptations of the emerging optical techniques by lowering high thresholds currently present in the new approaches.

A cyclometalated iridium(III) complex used as a conductor for the electrochemical sensing of IFN-γ

A novel iridium(III) complex was prepared and used as a conductor for sensitive and enzyme-free electrochemical detection of interferon gamma (IFN-γ). This assay is based on a dual signal amplification mechanism involving positively charged gold nanoparticles ((+)AuNPs) and hybridization chain reaction (HCR). To construct the sensor, nafion (Nf) and (+)AuNPs composite membrane was first immobilized onto the electrode surface. Subsequently, a loop-stem structured capture probe (CP) containing a special IFN-γ interact strand was modified onto the (+)AuNP surface via the formation of Au-S bonds. Upon addition of IFN-γ, the loop-stem structure of CP was opened, and the newly exposed "sticky" region of CP then hybridized with DNA hairpin-1 (H₁), which in turn opened its hairpin structure for hybridizing with DNA hairpin-2 (H₂). Happen of HCR between H₁ and H₂ thus generated a polymeric duplex DNA (dsDNA) chain. Meanwhile, the iridium(III) complex could interact with the grooves of the dsDNA polymer, producing a strong current signal that was proportional to IFN-γ concentration. Thus, sensitive detection of IFN-γ could be realized with a detection limit down to 16.3 fM. Moreover, satisfied results were achieved by using this method for the detection of IFN-γ in human serum samples.

Graphene and the immune system: Challenges and potentiality

In the growing area of nanomedicine, graphene-based materials (GBMs) are some of the most recent explored nanomaterials. For the majority of GBM applications in nanomedicine, the immune system plays a fundamental role. It is necessary to well understand the complexity of the interactions between GBMs, the immune cells, and the immune components and how they could be of advantage for novel effective diagnostic and therapeutic approaches. In this review, we aimed at painting the current picture of GBMs in the background of the immune system. The picture we have drawn looks like a cubist image, a sort of Picasso-like portrait looking at the topic from all perspectives: the challenges (due to the potential toxicity) and the potentiality like the conjugation of GBMs to biomolecules to develop advanced nanomedicine tools. In this context, we have described and discussed i) the impact of graphene on immune cells, ii) graphene as immunobiosensor, and iii) antibodies conjugated to graphene for tumor targeting. Thanks to the huge advances on graphene research, it seems realistic to hypothesize in the near future that some graphene immunoconjugates, endowed of defined immune properties, can go through preclinical test and be successfully used in nanomedicine.

Amperometric IFN-γ immunosensors with commercially fabricated PCB sensing electrodes

Lab-on-a-Chip (LoC) technology has the potential to revolutionize medical Point-of-Care diagnostics. Currently, considerable research efforts are focused on innovative production technologies that will make commercial upscaling of lab-on-chip products financially viable. Printed circuit board (PCB) manufacturing techniques have several advantages in this field. In this paper we focus on transferring a complete IFN-γ enzyme-linked immune-sorbent assay (ELISA) onto a commercial PCB electrochemical biosensing platform, We adapted a commercially available ELISA to detect the enzyme product TMB/H2O2 using amperometry, successfully reproducing the colorimetry-obtained ELISA standard curve. The results demonstrate the potential for the integration of these components into an automated, disposable, electronic ELISA Lab-on-PCB diagnostic platform.

An electrochemical aptasensor for detection of IFN-γ using graphene and a dual signal amplification strategy based on the exonuclease-mediated surface-initiated enzymatic polymerization

Tuberculosis is one of the major health problems in the world. The cytokine interferon γ (IFN-γ) is associated with the disease-specific immune responses and is used as a tuberculosis diagnosis marker. In this study, a novel electrochemical aptasensor was developed for IFN-γ detection based on the exonuclease-catalyzed target recycling and the TdT-mediated cascade signal amplification. To construct the aptasensor, a previously hybridized double-stranded DNA (capture probe hybridization with a complementary IFN-γ binding aptamer) was immobilized on a gold nanoparticle-graphene (Au-Gra) nanohybrid film-modified electrode. In the presence of IFN-γ, the formation of an aptamer-IFN-γ complex leads to the liberation of the aptamer from the double-stranded DNA (dsDNA). Using exonuclease, the aptamer was selectively digested, and IFN-γ was released for the target recycling. A large amount of single-stranded capture probes formed and led to the hybridization with signal probe-labelled Au@Fe3O4. Then, the labelled signal probe sequences were catalyzed at the 3'-OH group by terminal deoxynucleotidyl transferase (TdT) to form a long single-stranded DNA structure. As a result, the electron mediator hexaammineruthenium(III) chloride ([Ru(NH3)6](3+)) electrostatically adsorbed onto DNA producing a strong electrochemical signal which can be used to quantitatively measure the IFN-γ levels. With the conducting nanomaterial Au-Gra as a substrate and the target recycling-based surface-initiated enzymatic polymerization-mediated signal amplification strategy, the proposed aptasensor displayed a broad linearity with a low detection limit of 0.003 ng mL(-1). Moreover, the resulting aptasensor exhibited good specificity, acceptable reproducibility and stability, which makes this method versatile and suitable for detecting IFN-γ and other biomolecules.

Two-dimensional graphitic carbon nitride nanosheets for biosensing applications

Two-dimensional graphitic carbon nitride nanosheets (CNNSs) with planar graphene-like structure have stimulated increasingly research interest in recent years due to their unique physicochemical properties. CNNSs possess superior stability, high fluorescence quantum yield, low-toxicity, excellent biocompatibility, unique electroluminescent and photoelectrochemical properties, which make them appropriate candidates for biosensing. In this review, we first introduce the preparation and unique properties of CNNSs, with emphasis on their superior properties for biosensing. Then, recent advances of CNNSs in photoelectrochemical biosensing, electrochemiluminescence biosensing and fluorescence biosensing are highlighted. An additional attention is paid to the marriage of CNNSs and nucleic acids, which exhibits great potentials in both biosensing and intracellular imaging. Finally, current challenges and opportunities of this 2D material are outlined. Inspired by the unique properties of CNNSs and their advantages in biological applications, we expect that more attention will be drawn to this promising 2D material and extensive applications can be found in bioanalysis and diseases diagnosis.

Quantifying the effect of ionic screening with protein-decorated graphene transistors

Liquid-based applications of biomolecule-decorated field-effect transistors (FETs) range from biosensors to in vivo implants. A critical scientific challenge is to develop a quantitative understanding of the gating effect of charged biomolecules in ionic solution and how this influences the readout of the FETs. To address this issue, we fabricated protein-decorated graphene FETs and measured their electrical properties, specifically the shift in Dirac voltage, in solutions of varying ionic strength. We found excellent quantitative agreement with a model that accounts for both the graphene polarization charge and ionic screening of ions adsorbed on the graphene as well as charged amino acids associated with the immobilized protein. The technique and analysis presented here directly couple the charging status of bound biomolecules to readout of liquid-phase FETs fabricated with graphene or other two-dimensional materials.

A Graphene and Aptamer Based Liquid Gated FET-Like Electrochemical Biosensor to Detect Adenosine Triphosphate

Here we report successful demonstration of a FET-like electrochemical nano-biosensor to accurately detect ultralow concentrations of adenosine triphosphate. As a 2D material, graphene is a promising candidate due to its large surface area, biocompatibility, and demonstrated surface binding chemistries and has been employed as the conducting channel. A short 20-base DNA aptamer is used as the sensing element to ensure that the interaction between the analyte and the aptamer occurs within the Debye length of the electrolyte (PBS). Significant increase in the drain current with progressive addition of ATP is observed whereas for control experiments, no distinct change in the drain current occurs. The sensor is found to be highly sensitive in the nanomolar (nM) to micromolar ( μM) range with a high sensitivity of 2.55 μA (mM) (-1), a detection limit as low as 10 pM, and it has potential application in medical and biological settings to detect low traces of ATP. This simplistic design strategy can be further extended to efficiently detect a broad range of other target analytes.