Aptamer based label free thrombin assay based on the use of silver nanoparticles incorporated into self-polymerized dopamine

Chronoamperometric interrogation of an electrochemical aptamer-based sensor with tetrahedral DNA nanostructure pendulums for continuous biomarker measurements

Tetrahedral DNA nanostructure (TDN) is highly promising in developing electrochemical aptamer-based (E-AB) sensors for biomolecular detection, owing to its inherit programmability, spatial orientation and structural robustness. However, current interrogation strategies applied for TDN-based E-AB sensors, including enzyme-based amperometry, voltammetry, and electrochemical impedance spectroscopy, either require complicated probe design or suffer from limited applicability or selectivity. In this study, a TDN pendulum-empowered E-AB sensor interrogated by chronoamperometry for reagent-free and continuous monitoring of a blood clotting enzyme, thrombin, was developed. TDN pendulums with extended aptamer sequences at three vertices were immobilized on a gold electrode via a thiolated double-stranded DNA (dsDNA) at the fourth vertex, and their motion is modulated by the bonding of target thrombin to aptamers. We observed a significantly amplified signalling output on our sensor based on the TDN pendulum compared to E-AB sensors modified with linear pendulums. Moreover, our sensor achieved highly selective and rapidly responsive measurement of thrombin in both PBS and artificial urine, with a wide dynamic range from 1 pM to 10 nM. This study shows chronoamperometry-enabled continuous biomarker monitoring on a sub-second timescale with a drift-free baseline, demonstrating a novel approach to accurately detect molecular dynamics in real time.

Molecularly imprinted electrochemical biosensor for thrombin detection by comparing different monomers

Aim: Investigating molecularly imprinted polymers (MIPs) in electrochemical biosensors for thrombin detection, an essential protein biomarker. Comparing different monomers to showcase distinct sensitivity, specificity and stability advantages. Materials & methods: Dopamine, thionine and ethanolamine serve as monomers for MIP synthesis. Electrochemical methods and atomic force microscopy characterize sensor surfaces. Performance is evaluated, emphasizing monomer-specific electrochemical responses. Results: Monomer-specific electrochemical responses highlight dopamine's superior signal change and stability over 30 days. Notably, a low 5 pg/ml limit of detection, a broad linear range (5-200 pg/ml) and enhanced selectivity against interferents are observed. Conclusion: Dopamine-based MIPs show promise for high-performance electrochemical thrombin biosensors, suggesting significant applications in clinical diagnostics.

Metallic nanostructure-based aptasensors for robust detection of proteins

There is a significant need for fast, cost-effective, and highly sensitive protein target detection, particularly in the fields of food, environmental monitoring, and healthcare. The integration of high-affinity aptamers with metal-based nanomaterials has played a crucial role in advancing the development of innovative aptasensors tailored for the precise detection of specific proteins. Aptamers offer several advantages over commonly used molecular recognition methods, such as antibodies. Recently, a variety of metal-based aptasensors have been established. These metallic nanomaterials encompass noble metal nanoparticles, metal oxides, metal-carbon nanotubes, carbon quantum dots, graphene-conjugated metallic nanostructures, as well as their nanocomposites, metal-organic frameworks (MOFs), and MXenes. In general, these materials provide enhanced sensitivity through signal amplification and transduction mechanisms. This review primarily focuses on the advancement of aptasensors based on metallic materials for the highly sensitive detection of protein targets, including enzymes and growth factors. Additionally, it sheds light on the challenges encountered in this field and outlines future prospects. We firmly believe that this review will offer a comprehensive overview and fresh insights into metallic nanomaterials-based aptasensors and their capabilities, paving the way for the development of innovative point-of-care (POC) diagnostic devices.

Self-checking dual-modal aptasensor based on hybrid Z-scheme heterostructure of Zn-defective CdS/ZnS for oxytetracycline detection

Electrochemical detection methods have been widely used for trace target detection with satisfactory results. However, most of the existing electrochemical sensors rely only on single signal output, which inevitably suffer from the interference of the complex matrix of real samples. Herein, we proposed a dual-modal aptasensor for oxytetracycline assay with self-checking function by integrating photoelectrochemical (PEC) and electrochemical (EC) signal outputs in one analysis system. Zn-defective CdS/ZnS heterostructure was synthesized and served as the photo-electroactive substrate for constructing the biorecognition process, while methylene blue (MB) was used as a dual-functional probe to enhance both PEC and EC signals. Due to the high activity of Zn-defective CdS/ZnS heterojunction and the unique dual-modal signal readout strategy, the biosensing platform exhibits superior analytical performance with the relatively wide linear range (0.01-50 ng mL^-1), lower detection limits of 1.86 pg mL^-1 (PEC mode) and 3.08 pg mL^-1 (EC mode), as well as good selectivity, stability and reproducibility. The proposed dual-model analytical system with self-checking function is envisioned to provide a new approach for sensitive and reliable biosensing.

Recent Progresses in Development of Biosensors for Thrombin Detection

Thrombin is a serine protease with an essential role in homeostasis and blood coagulation. During vascular injuries, thrombin is generated from prothrombin, a plasma protein, to polymerize fibrinogen molecules into fibrin filaments. Moreover, thrombin is a potent stimulant for platelet activation, which causes blood clots to prevent bleeding. The rapid and sensitive detection of thrombin is important in biological analysis and clinical diagnosis. Hence, various biosensors for thrombin measurement have been developed. Biosensors are devices that produce a quantifiable signal from biological interactions in proportion to the concentration of a target analyte. An aptasensor is a biosensor in which a DNA or RNA aptamer has been used as a biological recognition element and can identify target molecules with a high degree of sensitivity and affinity. Designed biosensors could provide effective methods for the highly selective and specific detection of thrombin. This review has attempted to provide an update of the various biosensors proposed in the literature, which have been designed for thrombin detection. According to their various transducers, the constructions and compositions, the performance, benefits, and restrictions of each are summarized and compared.

Biomimetic synthesis of protein-DNA-CaHPO4 hybrid nanosheets for biosensing: Detection of thrombin as an example

Traditional strategies for coupling of proteins with DNA involve the additional modifications on protein or DNA to construct protein-DNA conjugates, resulting in complex or time-consuming coupling process. This study presented a biomimetic synthesis strategy to elaborately synthesize a new type of biomolecule-inorganic hybrid nanosheets. Horseradish peroxidase (HRP) and DNA aptamer can be easily combined with CaHPO₄ via coprecipitation simultaneously to form all-inclusive HRP-aptamer-CaHPO₄ hybrid (HAC) nanosheets integrating bifunction of biorecognition and signal amplification, which was proceeded in the green environment at room temperature and required no additional modifications on CaHPO₄, protein and DNA. Therefore, it avoided tedious linking and purification procedures. The HAC nanosheets were then employed as the signal labels and showed excellent performance for detecting thrombin. This bioinspired approach provides great possibilities to facile and efficient immobilization of protein, DNA or even other types of biomolecules (e.g., RNA and peptide) on inorganic nanomaterials and endows great potential in the preparation of a variety of multifunctional biomolecule-CaHPO₄ two-dimensional (2D) nanobiohybrids for various applications extending from biosensing to energy, biomedicine, environmental science and catalysis.

Nanomaterial-Based Label-Free Electrochemical Aptasensors for the Detection of Thrombin

Thrombin plays a central role in hemostasis and its imbalances in coagulation can lead to various pathologies. It is of clinical significance to develop a fast and accurate method for the quantitative detection of thrombin. Electrochemical aptasensors have the capability of combining the specific selectivity from aptamers with the extraordinary sensitivity from electrochemical techniques and thus have attracted considerable attention for the trace-level detection of thrombin. Nanomaterials and nanostructures can further enhance the performance of thrombin aptasensors to achieve high sensitivity, selectivity, and antifouling functions. In highlighting these material merits and their impacts on sensor performance, this paper reviews the most recent advances in label-free electrochemical aptasensors for thrombin detection, with an emphasis on nanomaterials and nanostructures utilized in sensor design and fabrication. The performance, advantages, and limitations of those aptasensors are summarized and compared according to their material structures and compositions.

Rational design of smart nano-platforms based on antifouling-nanomaterials toward multifunctional bioanalysis

The ability to design nanoprobe devices with the capability of quantitative/qualitative operation in complex media will probably underpin the main upcoming progress in healthcare research and development. However, the biomolecules abundances in real samples can considerably alter the interface performance, where unwanted adsorption/adhesion can block signal response and significantly decrease the specificity of the assay. Herein, this review firstly offers a brief outline of several significances of fabricating high-sensitivity and low-background interfaces to adjust various targets' behaviors induced via bioactive molecules on the surface. Besides, some important strategies to resist non-specific protein adsorption and cell adhesion, followed by imperative categories of antifouling reagents utilized in the construction of high-performance solid sensory interfaces, are discussed. The next section specifically highlights the various nanocomposite probes based on antifouling-nanomaterials for electrode modification containing carbon nanomaterials, noble metal nanoparticles, magnetic nanoparticles, polymer, and silicon-based materials in terms of nanoparticles, rods, or porous materials through optical or chemical strategies. We specially outline those nanoprobes that are capable of identification in complex media or those using new constructions/methods. Finally, the necessity and requirements for future advances in this emerging field are also presented, followed by opportunities and challenges.

l-Cysteine-Terminated Triangular Silver Nanoplates/MXene Nanosheets are Used as Electrochemical Biosensors for Efficiently Detecting 5-Hydroxytryptamine

5-Hydroxytryptamine (5-HT) is an important neurotransmitter, and its content in the human body is of great significance to human health. In this study, an l-cysteine-terminated triangular silver nanoplate loaded on a MXene (two-dimensional transition metal carbide or nitride) (Tri-AgNP/l-Cys/MXene) electrochemical sensor was used to detect 5-HT. As an electrically active amino acid with a sulfhydryl group, l-cysteine (l-Cys) forms a more stable Ag-S bond with silver nanoparticles, which can selectively substitute trisodium citrate (TSC) in TSC-capped triangular silver nanoplates (Tri-Ag-NP/TSC). Due to the good conductivity, biocompatibility, and large surface area, MXenes provide a good platform for loading Tri-AgNP/l-Cys. Under optimized conditions, the concentration range for detecting 5-HT with the sensor is 0.5-150 μM, and the limit of detection (LOD) is 0.08 μM (S/N = 3). For detecting 5-HT in actual serum samples, the sensor also showed a good recovery rate (95.38-102.3%), and the relative standard deviation was 2.2-3.4%.

Gold nanostructured laser-scribed graphene: A new electrochemical biosensing platform for potential point-of-care testing of disease biomarkers

Improvements in the laser-scribed graphene (LSG)-based electrodes are critical to overcoming limitations of bare LSG electrodes in terms of sensitivity, direct immobilization of detection probes for biosensor fabrication, and ease of integration with point-of-care (POC) devices. Herein, we introduce a new class of nanostructured gold modified LSG (LSG-AuNS) electrochemical sensing system comprising LSG-AuNS working electrode, LSG reference, and LSG counter electrode. LSG-AuNS electrodes are realized by electrodeposition of gold chloride (HAuCl₄) solution, which gave~2-fold enhancement in sensitivity and electrocatalytic activity compared to bare LSG electrode and commercially available screen-printed gold electrode (SPAuE). We demonstrate LSG-AuNS electrochemical aptasensor for detecting human epidermal growth factor receptor 2 (Her-2) with a limit of detection (LOD) of 0.008 ng/mL and a linear range of 0.1-200 ng/mL. LSG-AuNS-aptasensor can easily detect different concentrations of Her-2 spiked in undiluted human serum. Finally, to show the LSG-AuNS sensor system's potential to develop POC biosensor devices, we integrated LSG-AuNS electrodes with a handheld electrochemical system operated using a custom-developed mobile application.

From Small Molecules Toward Whole Cells Detection: Application of Electrochemical Aptasensors in Modern Medical Diagnostics

This paper focuses on the current state of art as well as on future trends in electrochemical aptasensors application in medical diagnostics. The origin of aptamers is presented along with the description of the process known as SELEX. This is followed by the description of the broad spectrum of aptamer-based sensors for the electrochemical detection of various diagnostically relevant analytes, including metal cations, abused drugs, neurotransmitters, cancer, cardiac and coagulation biomarkers, circulating tumor cells, and viruses. We described also possible future perspectives of aptasensors development. This concerns (i) the approaches to lowering the detection limit and improvement of the electrochemical aptasensors selectivity by application of the hybrid aptamer-antibody receptor layers and/or nanomaterials; and (ii) electrochemical aptasensors integration with more advanced microfluidic devices as user-friendly medical instruments for medical diagnostic of the future.

Electrodes Based on a Titanium Dioxide Nanotube-Spherical Silver Nanoparticle Composite for Sensing of Proteins

The aim of the research was to provide electrochemical, chemical, phase, and microscopic characteristics of electrodes based on titanium dioxide nanotubes (TNTs) containing uniformly deposited, nonagglomerated spherical silver nanoparticles (AgNPs). The nanoparticles were produced with the use of electrodeposition and sputter deposition methods. This paper presents the results of research of these platforms with the use of the following techniques: electrochemical impedance spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, and scanning electron microscopy. Evaluation of the adsorption of proteins-bovine serum albumin (BSA)-was carried out to establish the possibility of the use of the electrodes in a low-cost, simple detection system without surface functionalization. The research proved that the AgNP deposition facilitated the electron transfer increasing their conductivity properties as well as promoting the protein adsorption. The AgNPs/TNT electrodes showed a high selectivity to the BSA-anti-BSA complex. Half an hour of immobilization was enough to completely saturate the TNT electrodes, whereas for AgNPs/TNTs, 1 h of immobilization seemed to be not enough. The impedance parameter changes for electrodes with the AgNPs reached even about 300%. The biggest changes were noted for the platform obtained using cyclic voltammetry, so it is the best detection platform for biosensing.

Recent Advances in Electrochemical Sensors for the Detection of Biomolecules and Whole Cells

Electrochemical sensors are considered an auspicious tool to detect biomolecules (e.g., DNA, proteins, and lipids), which are valuable sources for the early diagnosis of diseases and disorders. Advances in electrochemical sensing platforms have enabled the development of a new type of biosensor, enabling label-free, non-destructive detection of viability, function, and the genetic signature of whole cells. Numerous studies have attempted to enhance both the sensitivity and selectivity of electrochemical sensors, which are the most critical parameters for assessing sensor performance. Various nanomaterials, including metal nanoparticles, carbon nanotubes, graphene and its derivatives, and metal oxide nanoparticles, have been used to improve the electrical conductivity and electrocatalytic properties of working electrodes, increasing sensor sensitivity. Further modifications have been implemented to advance sensor platform selectivity and biocompatibility using biomaterials such as antibodies, aptamers, extracellular matrix (ECM) proteins, and peptide composites. This paper summarizes recent electrochemical sensors designed to detect target biomolecules and animal cells (cancer cells and stem cells). We hope that this review will inspire researchers to increase their efforts to accelerate biosensor progress-enabling a prosperous future in regenerative medicine and the biomedical industry.

Ultra-sensitive and selective electrochemical biosensor with aptamer recognition surface based on polymer quantum dots and C60/MWCNTs- polyethylenimine nanocomposites for analysis of thrombin protein

In this study, an ultra-sensitive and selective Thrombin biosensor with aptamer-recognition surface is introduced based on carbon nanocomposite. To prepare the this biosensor, screen-printed carbon electrodes (SPCE) were modified with a nanocomposite made from fullerene (C₆₀), multi-walled carbon nanotubes (MWCNTs), polyethylenimine (PEI) and polymer quantum dots (PQdot). The unique characteristics of each component of the C₆₀/MWCNTs-PEI/PQdot nanocomposite allow for synergy between nanoparticles while polymer quantum dots resulted in characteristics such as high stability, high surface to volume ratio, high electrical conductivity, high biocompatibility, and high mechanical and chemical stability. The large number of amine groups in C₆₀/MWCNTs-PEI/PQdot nanocomposite created more sites for better covalent immobilization of amino-linked aptamer (APT) which improved the sensitivity and stability of the aptasensor. Differential Pulse Voltammetry (DPV) method with probe solution was used as the measurment method. Binding of thrombin protein to aptamers immobilized on the transducer resulted in reduced electron transfer at the electrode/electrolyte interface which reduces the peak current (I_P) in DPV. The calibration curve was drawn using the changes in the peak current (ΔI_P),. The proposed aptasensor has a very low detection limit of 6 fmol L^-1, and a large linear range of 50 fmol L^-1 to 20 nmol L^-1. Furthermore, the proposed C₆₀/MWCNTs-PEI/PQdot/APT aptasensor has good reproducibility, great selectivity, low response time and a good stability during its storage. Finally, the application of the proposed aptasensor for measuring thrombin on human blood serum samples was investigated. This aptasensor can be useful in bioengineering and biomedicine applications as well as for clinical studies.

Silver nanoparticles conjugated MnFe-based Prussian blue analogue for voltammetric and impedimetric bioaptasensing of amifostine (ethyol)

A novel bioaptasensing-based electrochemical method for determination of amifostine (AMF) is proposed. The electrochemical aptasensor is based on modification of a glassy carbon electrode with a nanocomposite consisting of silver nanoparticles @ MnFe Prussian blue analogue nanospheres (AgNPs@MnFePBA NS), followed by immobilization of aptamer via Ag-N bonds (aptamer/AgNPs@MnFePBA NS/GCE). Experimental parameters including pH, incubation time, and aptamer concentrations were optimized. Electrochemical impedance spectroscopy (EIS) and differential pulse voltammetric (DPV) techniques were utilized to quantify AMF. The anodic peak current (∆Ipa) and charge transfer resistance (∆Rct) differences increase in the presence of AMF. Under the optimal conditions, using the redox probe, the electrochemical aptasensor exhibited linear ranges of 0.34-45 nmol L^-1 and 0.69-45 nmol L^-1 with LODs of 0.11 nmol L^-1 and 0.23 nmol L^-1 for EIS and DPV, respectively. The aptasensor was used to determine AMF in human plasma and in the presence of interfering species with recoveries and RSDs in the range 97.8-103.2% and 2.2-4.2%, respectively. Graphical abstract.

A fluorometric assay of thrombin using magnetic nanoparticles and enzyme-free hybridization chain reaction

A fluorescence method based on functionalized magnetic nanoparticles (FMNPs) and hybridization chain reaction (HCR) is developed for the enzyme-free amplified determination of thrombin. In the proposed design, aptamer against thrombin was hybridized with the capture DNA-modified magnetic nanoparticles to yield the FMNPs. In the presence of thrombin, aptamers are released due to the specific and high-affinity binding between thrombin and its aptamer. The exposed capture DNA subsequently hybridized with the partial sequence of helper DNA, and the vacant sequence of helper DNA further hybridized with HCR products which is pre-formed by the alternate hybridization of single-stranded DNAs (H1 and H2). The immobilized HCR products were then labeled with YOYO-1 for fluorescence measurement. Fluorescence signal intensity of labeled YOYO-1 was measured at an emission wavelength of 519 nm (excitation under 488 nm) and used for calibration. By taking advantage of HCR amplification, this direct assay strategy showed a linear response in the 20- to 200-pM concentration range, and the limit of detection is 9.2 pM which is about 3-orders of magnitude lower than the serum thrombin concentration (10 nM) that triggers blood clotting. This developed method can efficiently differentiate the target protein from a protein matrix, and it is verified by determination of thrombin in spiked serum samples with recoveries in the range of 94.5-103.3%. Graphical abstract A fluorometry method for thrombin detection using magnetic nanoparticles and enzyme-free hybridization chain reaction.

Electrochemiluminescence methods using CdS quantum dots in aptamer-based thrombin biosensors: a comparative study

The detection of thrombin by using CdS nanocrystals (CdS NCs), gold nanoparticles (AuNPs) and luminol is investigated in this work. Thrombin is detected by three methods. One is called the quenching method. It is based on the quenching effect of AuNPs on the yellow fluorescence of CdS NCs (with excitation/emission wavelengths of 355/550 nm) when placed adjacent to CdS NCs. The second method (called amplification method) is based on an amplification mechanism in which the plasmonics on the AuNPs enhance the emission of CdS NCs through distance related Förster resonance energy transfer (FRET). The third method is ratiometric and based on the emission by two luminophores, viz. CdS NCs and luminol. In this method, by increasing the concentration of thrombin, the intensity of CdS NCs decreases, while that of luminol increases. The results showed that ratiometric method was most sensitive (with an LOD of 500 fg.mL^-1), followed by the amplification method (6.5 pg.mL^-1) and the quenching method (92 pg.mL^-1). Hence, the latter is less useful. Graphical abstract Schematic representation of three different methods (quenching, amplification and ratiometric) were applied for detection of thrombin via aptasensor. The CdS nanocrystals, streptavidin (Str) coated AuNPs and also Str-luminol coated AuNPs were used for the construction steps of the electrochemiluminescence (ECL)-based biosensor.

Influence of the Silver Nanoparticles (AgNPs) Formation Conditions onto Titanium Dioxide (TiO2) Nanotubes Based Electrodes on Their Impedimetric Response

This paper presents the comparison of the effects of three methods of production of silver spherical and near-spherical nanoparticles (AgNPs) on the titanium dioxide nanotubes (TNT) base: cyclic voltammetry, chronoamperometry, and sputter deposition. It also evaluates the influence of silver nanoparticles on the electrochemical properties of the developed electrodes. The novelty of this research was to fabricate regular AgNPs free of agglomerates uniformly distributed onto the TNT layer, which has not been accomplished with previous attempts. The applied methods do not require stabilizing and reducing reagents. The extensive electrochemical characteristic of AgNP/TNT was performed by open circuit potential and electrochemical impedance spectroscopy methods. For AgNPs/TNT obtained by each method, the impedance module of these electrodes was up to 50% lower when compared to TNT, which means that AgNPs enabled more efficient electron transfer due to the effective area increase. In addition, the presence of nanoparticles increases the corrosion resistance of the prepared electrodes. These substrates can be used as electrochemical sensors due to their high electrical conductivity, and also as implants due to the antibacterial properties of both the TNT and AgNPs.

Electrochemical aptasensor based on conductive supramolecular polymer hydrogels for thrombin detection with high selectivity

Herein, we synthesized a kind of conductive supramolecular polymer hydrogel (CSPH) based on polyaniline (PANI) which can not only improve the conductivity but also promote antifouling performance of the aptasensor for the specific recruitment of thrombin (TB) from complex samples. With the electrochemical copolymerization of aniline (AN) and 3-aminophenylboronic acid (ABA) on glassy carbon electrode (GCE), the electrode was then inserted into the polyvinyl alcohol (PVA) solution to obtain robust CSPH through boric acid groups incorporated onto PANI to cause gelation of PVA solution, owing to the hydrophilicity of CSPH and nearly electrical neutrality, the modified electrode is antifouling without integration of other antifouling materials. A sandwich-type electrochemical aptasensor was constructed on the CSPH based electrode interfaces. Thrombin aptamer 1 (TBA1) were modified on the CSPH through amide bond, and thrombin aptamer 2 modified magnetic nanoparticles (MNP-TBA2) are used as signal amplification probes, the aptasensor has good sensitivity with a linear range from 1 pmol/L to 10 nmol/L and has a detection limit down to 0.64 pmol/L. The strategy of utilizing eletropolymerization of CSPH films to undergo highly selective thrombin recognition is, of course, readily extended to a broad range of targets in the real samples, and the recovery was ranging from 95.2% to 106.3% and RSDs varying from 2.3% to 4.5%.

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.

An aptasensor for troponin I based on the aggregation-induced electrochemiluminescence of nanoparticles prepared from a cyclometallated iridium(III) complex and poly(4-vinylpyridine-co-styrene) deposited on nitrogen-doped graphene

An ultrasensitive electrochemiluminescence (ECL) disposable aptamer sensor (aptasensor) is presented for detection of myocardial infarction biomarker by quantification of troponin I in blood serum. A screen-printed electrode was modified with (a) aptamer-modified gold nanoparticles, (b) cyclometallated iridium(III)-poly-4-vinylpyridine nanoparticles, and (c) nitrogen-doped graphene in order to increase the loading capacity and conductivity of the aptasensor. If the aptasensor is exposed to troponin I, it will bind to the aptamer and desorb the aptamer from gold nanoparticles and the surface of the electrode. This generates an enhancement in ECL emission depending on troponin I concentration. ECL emission is strongly improved by aggregation-induced phenomenon, which is caused by inhibition of the water and oxygen quenching effect on the iridium complex ECL in aqueous media. Under optimum conditions, the aptasensor has a wide dynamic range that extends from 0.1 pM to 10 nM, with a 20 fM detection limit (S/N = 3) and a relative standard deviation of 3.1%. The ECL aptasensor was successfully applied to 20 individual human serum for the detection of troponin I biomarker. Graphical abstract Schematic presentation of electrochemiluminescence aptamer assay fabrication for detection of Troponin I. Carbon screen printed electrode (CSPE) was modified with nitrogen doped graphene (NG), gold nanoparticles (AuNPs), cyclometallated iridium(III)-polyvinylpyridine polymer nanoparticles, ionic liquid and bovine serum albumin.

Voltammetric kanamycin aptasensor based on the use of thionine incorporated into Au@Pt core-shell nanoparticles

A signal-on aptasensor is described for the voltammetric determination of kanamycin (KANA). Au@Pt core-shell nanoparticles with large surface and good electrical conductivity were synthetized and act as both a conductive material and as the carrier for complementary strands (CS2) and thionine (TH). In the presence of KANA, the electrochemical response of TH changes due to hybridization between CS1 immobilized on the electrode and the Au@Pt-CS2/TH system. The peak current increases linearly with the logarithm of the KANA concentration in the range from 1 pM to 1 μM, and the limit of detection is 0.16 pM. The sensor was characterized in terms of selectivity, reproducibility and stability, and satisfactory results were obtained. It was also utilized for the determination of KANA in (spiked) chicken samples. The recoveries (95.8-103.2%) demonstrate the potential of the method for KANA detection in real samples. Graphical abstract A signal-on aptasensor for kanamycin (KANA) was developed by using Au@Pt core-shell nanoparticles as nanocarrier for probe aptamer and as a sensing probe.

Ultrasensitive determination of thrombin by using an electrode modified with WSe2 and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase

A sensitive aptamer/protein binding-triggered sandwich assay for thrombin is described. It is based on electrochemical-chemical-chemical redox cycling using a glassy carbon electrode (GCE) that was modified with WSe₂ and gold nanoparticles (AuNPs). The AuNPs are linked to thrombin aptamer 1 via Au-S bonds. Thrombin is first captured by aptamer 1 and then sandwiched through the simultaneous interaction with AuNPs modified with thrombin-specific aptamer 2 and signalling probe. Subsequently, the DNA-linked AuNP hybrids result in the capture of streptavidin-conjugated alkaline phosphatase onto the modified GCE through the specific affinity reaction for further signal enhancement. As a result, a linear range of 0-1 ng mL^-1 and a detection limit as low as 190 fg mL^-1 are accomplished. The specificity for thrombin is excellent. Conceivably, this strategy can be easily expanded to other proteins by using the appropriate aptamer. Graphical abstract Schematic presentation of an electrochemical biosensor for thrombin based on WSe₂ and gold nanoparticles, aptamer-thrombin-aptamer sandwiching, redox cycling, and signal enhancement by alkaline phosphatase.