Thrombin Aptasensor Research Articles

Cu-Ag nanoparticles-dispersed and microchannel textured-laser induced graphene: A chemiresistive aptasensor for thrombin

Thrombin is a key enzyme of the clotting cascade, which can convert soluble fibrinogen to insoluble fibrin. A rapid and accurate sensor is required to give easy access to patients and healthy individuals to monitor their thrombin levels. In this study, a Cu and Ag bimetal nanoparticles (NPs)-dispersed and microchannel textured-laser induced graphene (Cu-Ag-LIG)-based chemiresistive aptasensor is developed. The sensor substrate was synthesized via the suspension polymerization of phenol and formaldehyde, with the in situ inclusion of the metal salts in the reaction mixture. Laser ablation converted the carbon containing polymeric groups to sp2 hybridized graphitic carbon and the metal salts to zero-valent metal NPs. Laser ablation was also used to create microchannels on the graphene surface to ensure the uniform distribution of the analyte. Ag NPs facilitated the binding of thrombin binding aptamer (TBA) via covalent bond, while Cu NPs provided structural support. The aptasensor showed a linear response over the 0.1 – 50 units/mL-thrombin concentration range. The sensor response was unaffected by common interfering biomolecules such as glucose, bovine serum albumin, urea, trypsin, and cholesterol. This study showcases the broader and often overlooked significance of chemiresistive sensors not only in healthcare but also across various scientific domains, offering avenues for transformative advancements in diagnostic technologies.

Hemin/G-quadruplex and AuNPs-MoS2 based novel dual signal amplification strategy for ultrasensitively sandwich-type electrochemical thrombin aptasensor

In this work, a novel sandwich-type electrochemical aptasensor based on the dual signal amplification strategy of hemin/G-quadruplex and AuNPs-MoS2 was designed and constructed, which realized the highly sensitive and specific detection of thrombin (TB). In this aptasensor, the 15-mer TB-binding aptamer (TBA-1) modified with thiol group was immobilized on the surface of AuNPs modified glassy carbon electrode (AuNPs/GCE) as capturing elements. Another thiol-modified 29-mer TB-binding aptamer (TBA-2) sequence containing G-quadruplex structure for hemin immobilization was designed. The formed hemin/G-quadruplex/TBA-2 sequence was further combined to the AuNPs decorated flower-like molybdenum disulfide (AuNPs-MoS2) composite surface via Au-S bonds, acting the role of reporter probe. In presence of the target TB, the sandwich-type electrochemical aptamer detection system could be formed properly. With the assistance of the dual signal amplification of AuNPs-MoS2 and hemin/G-quadruplex toward H2O2 reduction, the sandwich-type electrochemical aptasensor was successfully constructed for sensitive detection of TB. The results demonstrate that the fabricated aptasensor displays a wide linear range of 1.0 × 10−6 ∼ 10.0 nM with a low detection limit of 0.34 fM. This proposed aptasensor shows potential application in the detection of TB content in real biological samples with high sensitivity, selectivity, and reliability.

PEC thrombin aptasensor based on Ag–Ag2S decorated hematite photoanode with signal-down effect of precipitation catalyzed by G-quadruplexes/hemin

A photoelectrochemical (PEC) aptasensor for thrombin detection was rationally designed based on the photoanode of one-dimensional hematite nanorods (α-Fe2O3 NRs) with several steps of modifications. Uniform α-Fe2O3 NRs were grown vertically on the surface of fluorine-doped tin oxide (FTO) conductive glass through a one-step hydrothermal method; then Ag was grown on the surface of α-Fe2O3 NRs through a photoreduction method followed by a partial in-situ transformation into Ag2S, conferring an improvement on the initial photocurrent. Two main critical factors, namely, the steric hindrance of thrombin, benzoquinone (BQ) precipitation oxidized by H2O2 under the catalysis of G-quadruplexes/hemin, contributed to the sensitive signal-down response toward the target. Photocurrent signals related with thrombin concentration was established for thrombin analysis due to the non-conductive complex as well as their competitive consumption of electron donors and irradiation light. The excellent initial photocurrent was combined with the signal-down amplification in the design of the biosensor, conferring a limit of detection (LOD) as low as 40.2 fM and a wide linear range from 0.0001 nM to 50 nM for the detection of thrombin. The proposed biosensor was also assessed in terms of selectivity, stability, and applicability in human serum analyses, which provided an appealing maneuver for the specific analysis of thrombin in trace amount.

Target-Synergized Biologically Mediated RAFT Polymerization for Electrochemical Aptasensing of Femtomolar Thrombin.

The assay of thrombin levels is integral to the assessment of coagulation function and clinical screening of coagulation disorder-related diseases. In this work, we illustrate the ingenious use of the target-synergized biologically mediated reversible addition-fragmentation chain transfer (RAFT) polymerization (tsBMRP) as a novel amplification strategy for the electrochemical aptamer-based biosensing of thrombin at the femtomolar levels. Briefly, the tsBMRP-based strategy relies on the boronate affinity-mediated decoration of the glycan chain(s) of the target itself with RAFT agents and the subsequent recruitment of signal labels via BMRP, mediated by the direct reduction of RAFT agents by NADH into initiating/propagating radicals. Obviously, the tsBMRP-based strategy is biologically friendly, low-cost, and simple in operation. As thrombin is a glycoconjugate, its electrochemical aptasensing involves the use of the thrombin-binding aptamer (TBA) as the recognition receptor, the site-specific decoration of RAFT agents to the glycan chain of thrombin via boronate affinity, and further the recruitment of ferrocene signal labels via the BMRP of ferrocenylmethyl methacrylate (FcMMA). As boronate affinity results in the decoration of each glycan chain with tens of RAFT agents while BMRP recruits hundreds of signal labels to each RAFT agent-decorated site, the tsBMRP-based strategy allows us to detect thrombin at a concentration of 35.3 fM. This electrochemical aptasensor is highly selective, and its applicability to thrombin detection in serum samples has been further demonstrated. The merits of high sensitivity and selectivity, low cost, good anti-interference capability, and simple operation make the tsBMRP-based electrochemical thrombin aptasensor great promise in biomedical and clinical applications.

Enzyme‐free Recycling Amplification‐based Sensitive Electrochemical Thrombin Aptasensor

AbstractIn this work, an enzyme‐free recycling amplification‐based sensitive electrochemical thrombin aptasensor using catalytic hairpin assembly (CHA) and bisferrocene was proposed for electrochemical beacon. Thrombin triggered the CHA reaction that in turn formed a number of double‐stranded complexes,which are fixed on the surface of the gold electrode through potential‐assisted Au−S deposition, and a large number of labeled bisferrocene are placed close to the gold electrode to generate electrochemical signal. The linear range of the electrochemical sensor was 0.25 pM‐2.5 nM for thrombin with detection limit of 0.18 pM. This sensor can be employed to monitor the thrombin in human serum samples.

A Sensitive Thrombin Aptasensor Based on Target Circulation Strategy.

A convenient homogeneous electrochemical thrombin sensor based on potential-assisted Au-S deposition and a dual signal amplification strategy was established in this study. Potential-assisted Au-S deposition does not require the modification of the gold electrode, thus eliminating the tedious pre-modification of the electrode. To better amplify the output signal, both ends of the signal hairpin probes were modified with a new electroactive substance, tetraferrocene, which was synthesized by the authors. Thrombin was immediately hybridized with a thiol-modified probe to open the stem-loop structure. After chain hybridization, thrombin was replaced and participated in the next round of the reaction; thus, the cascade amplification of the signal was realized. The hybrid chain formed an Au-S deposition under potential assistance, and the electrochemical signal of tetraferrocene could then be measured through differential pulse voltammetry (DPV) and consequently used for the quantitative detection of target thrombin. In addition, the detection limit of thrombin was as low as 0.06 pmol/L, and the detection of common interfering proteins was highly specific.

Electrochemical sandwich-type thrombin aptasensor based on silver nanowires& particles decorated electrode and the signal amplifier of Pt loaded hollow zinc ferrite

An ultrasensitive enzyme-free electrochemical sandwich-type thrombin aptasensor is proposed in this work, with the amplifier of Pt loaded hollow zinc ferrite nanospheres. Silver nanowires& particles (AgNWs&PCs) are used as the substrate materials to decorate the working electrode. Silver particles (AgPCs) are introduced for welding of AgNWs to further improve the electrical performance of the working electrode. The conductive electrode decorated with AgNWs&PCs can provide a substrate for the immobilization of thrombin aptamer 1 (Apt1). Moreover, AgNWs&PCs possess the catalytic activity for H2O2 reduction, contributing to the signal amplification. The prepared Pt loaded hollow zinc ferrite nanospheres with an excellent electrocatalytic activity for H2O2 reduction can also be used to immobilize aptamer 2 (Apt2). Under the optimized condition, the performance of the biosensor is evaluated by amperometry. The proposed thrombin aptasensor has a wide linear detection range from 0.05 pM to 35 nM and a low detection limit of 0.016 pM (S/N = 3), due to the synergistic effect of AgNWs&PCs electrode and the Pt loaded hollow zinc ferrite nanospheres amplifier. This aptasensor displays high sensitivity, good reproducibility and stability, providing a promising platform for the analysis of thrombin.

Self-assembled perylenetetracarboxylic acid-reduced graphene oxide film for high-sensitive impedimetric determination of thrombin

Graphene-based thin film has been widely used as signal conductor and platform material in electrochemical sensors. For commonly used reduced graphene oxide (rGO), oxygen-containing functional groups can provide coupling sites to conjugate with bio-cognitive elements, but high degree of oxidation can harm its structural integrity and signal conductivity. In this work, a new strategy is developed to balance the conductivity and functionality of rGO. The PTCA-rGO composite film was prepared by self-assembly and used to fabricate electrochemical biosensor. To form reusable thrombin aptasensor, an in situ layer-by-layer self-assembling method was adopted to stepwise deposit reduced graphene oxide (rGO), 3, 4, 9, 10-perylenetetracarboxylic acid (PTCA), and thrombin aptamer (TBA) onto 3-aminopropyltriethoxy silane (APTES)-modified glassy carbon electrode (GCE). The as-prepared aptasensor was used to determine thrombin in response to impedimetric signal by electrochemical impedance spectroscopy (EIS). The as-prepared GCE/rGO/PTCA/TBA sensor provided outstanding performance for determination of thrombin concentration with wide linear range (1 pM-100 nM), low detection limit (0.2 pM), reusability, and good specificity to thrombin. The good performance of GCE/rGO/PTCA/TBA aptasensor can be attributed to the electrochemical property of rGO-PTCA composite film and the in situ layer-by-layer fabricated strategy. This PTCA-modification method is promising to be widely used in the fabrication of graphene-based electrochemical devices.

Visible light driven photoelectrochemical thrombin aptasensor based on uniform TiO2 nanotube arrays modified with CuOx and perylene-3,4,9,10-tetracarboxylic acid

In this work, a sensitive signal-off photoelectrochemical (PEC) thrombin aptasensor with satisfying specificity is proposed, in which the evident initial photocurrent response is produced by the photoanode and the signal amplification strategy toward the target is based on the specific bio-affinity properties between thrombin and their aptamers. The photoanode was fabricated with uniform TiO2 nanotube arrays decorated with CuOx and perylene-3,4,9,10-tetracarboxylic acid (PTCA). After the decoration of CuOx and PTCA, both possessing a strong absorption in visible region, the photocurrent response is improved greatly. Pt nanoparticles were modified on the photoanode electrode to immobilize thrombin aptamers, which could obviously improve the conductivity of the photoanode electrode owing to the excellent conductivity of Pt nanoparticles. The non-conductive complex leads to dramatical decrease in the photocurrent value due to the steric hinder effect. Based on the joint action of evident photocurrent response of photoanode and significant signal amplification strategy, the aptasensor in this project offers a wide linear range from 0.0003 nM to 10 nM, with a detection limit (3S/N) of thrombin down to 55 fM. Moreover, the as-fabricated aptasensor exhibits acceptable selectivity and stability, providing a meaningful attempt for the detection of thrombin.

Photoelectrochemical aptasensor for thrombin based on Au-rGO-CuS as signal amplification elements.

A photoelectrochemical platform for thrombin determination was developed based on Au-rGO-CuS as multiple signal amplification elements. CuInS2 QDs was used to sensitize burr-shape TiO2 (b-TiO2) to obtain astrong photocurrent. Under the specific recognition between aptamer and thrombin, asandwichlike structure was formed and theAu-rGO-CuS-labeled aptamer (S2@Au-rGO-CuS) was immobilized on the electrodesurface. This induced a sharp decrease in photocurrent. The phenomenonis mainly due to the factthat CuS NPs can competitively consume the light energy and electron donor with CuInS2/b-TiO2. The rGO can increase the amount of CuS NPs and the Au NPs can accelerate charge transferring which depress the recombination of photogenerated electrons and holes in CuS to further enhance the competitive capacity of CuS. Thesandwichlike structure has asteric hindrance effect. Therefore,the S2@Au-rGO-CuS hasamultiple signal amplification function for thrombin determination. Under optimal conditions, the PEC aptasensor exhibited a wide linear concentration range from 0.1pM to 10nM with a low detection limit of 30fM (S/N= 3) for thrombin. Besides, the designed aptasensor performed well in the assay of human serum sample, indicating good potential for the determination of thrombin in real samples. Graphical abstract.

An electrochemical thrombin aptasensor based on the use of graphite-like C3N4 modified with silver nanoparticles.

An electrochemical aptasensor for thrombin is introduced that makes use of a nanohybrid composed of silver nanoparticles and graphite-like carbon nitride (Ag-g-C3N4). The material has a large surface and good biocompatibility. AgNPs are modified directly on the surface of g-C3N4 via chemical reduction. A glass carbon electrode (GCE) modified with Ag-g-C3N4 can immobilize a large number of amino-terminated thrombin binding aptamers (NH2-TBA) through strong Ag-N bonds. The electrochemical impedance signal of the aptasensor increases in the presence of thrombin. Under the optimal conditions and by using[Fe(CN)6]3-/4- as an electrochemical probe, the aptasensor shows a wide linear range of 100 fM - 20nM with a lower detection limit of 38 fM. The method was applied to the determination of thrombin in spiked human plasma and the recoveries fluctuated from 97.2% to 103%. Graphical abstractSchematic representation of an electrochemical aptasensor using graphite-like carbon nitride (C3N4) modified with silver nanoparticles as electrode substrate for thrombin (TB) detection.

Highly Enhanced Electrochemiluminescence Luminophore Generated by Zeolitic Imidazole Framework-8-Linked Porphyrin and Its Application for Thrombin Detection.

Novel and distinct enhancement in electrochemiluminescence (ECL) signals of advanced organic luminophores are of importance for expanding their applications in early diagnosis. This work reported the construction of an ultrasensitive label-free ECL aptasensor for thrombin (TB) detection by grafting zinc proto-porphyrin IX (ZnP) onto an aminated zeolitic imidazole framework-8 (defined as ZnP-NH-ZIF-8 for clarity) as the luminophore. The structure and optical properties of the resulting ZnP-NH-ZIF-8 were carefully characterized. For that, there appeared to be weak ECL radiation for ZnP in dichloromethane (DCM) containing tetra-n-butylammonium perchlorate (TBAP) because of the as-formed singlet-state oxygen via the "reduction-oxidation" route. More notably, the ECL signals display 153-times enhancement for ZnP-NH-ZIF-8, thanks to the excellent catalytic kinetics for the oxygen reduction reaction (ORR). By virtue of the specific interactions of the TB aptamer (TBA) with the TB protein and the highly efficient catalysis of the ZnP-NH-ZIF-8 for ORR, the as-prepared aptasensor showed a wider linear range (0.1 fM∼1 pM) and a lower detection limit (ca. 58.6 aM). This work provides some useful guidelines for synthesis of an advanced organic luminophore with largely boosted ECL signals in ultrasensitive analysis and clinical diagnosis.

An Ultrasensitive Electrochemical Aptasensor for Thrombin Detection Using MoS2 Nanoparticles Loaded Iron-Porphyrinic Metal-Organic Framework as Signal Amplifier

An ultrasensitive electrochemical aptasensor for thrombin (TB) was designed using MoS2 nanoparticles loaded iron-porphyrinic metal-organic framework (PCN-223-Fe) as the electrochemical tracer. Spindle-shaped PCN-223-Fe was synthesized with zirconium ion as node and iron-porphyrin as linker, and in situ loaded with MoS2 nanoparticles to obtain MoS2/PCN-223-Fe composite. MoS2/PCN-223-Fe was characterized by electron microscopies, X-ray diffraction and X-ray photoelectron spectroscopy. Due to the synergistic effect of MoS2 and PCN-223-Fe, MoS2/PCN-223-Fe modified electrode exhibited enhanced electrocatalytic activity to oxygen reduction. Sequentially, MoS2/PCN-223-Fe was combined with TB aptamer 2 to prepare signal probe. A sandwich-type electrochemical aptasensor was constructed for TB detection. TB aptamer 1 was fixed on electrode surface to capture TB molecules, and then TB aptamer 2 functionalized MoS2/PCN-223-Fe tracer was introduced on electrode surface. By detecting the electrochemical signal of oxygen reduction catalyzed by MoS2/PCN-223-Fe, the designed TB sensor was monitored. The proposed TB aptasensor showed a wide linear range from 0.1 pM to 100 nM and a low detection limit of 0.03 pM (S/N = 3). Meanwhile, the aptasensor showed good reproducibility, stability and selectivity, which was successfully applied for TB detection in human serum sample. This strategy broadens application of metal-organic frameworks, and could be used for other biomolecules detection.

An aptasensor for the label-free detection of thrombin based on turn-on fluorescent DNA-templated Cu/Ag nanoclusters.

A highly sensitive thrombin aptasensor was constructed based on the alteration of the aptamer conformation induced by the target recognition and the turn-on fluorescence due to the proximity of two darkish DNA-templated copper/silver nanoclusters (DNA-Cu/Ag NCs). Two DNA templates were designed as the functional structures consisting of the Cu/Ag NC-nucleation segment located at two termini or one terminus and the aptamer segment in the middle of a DNA template. Two darkish DNA-Cu/Ag NCs came close to each other when the aptamer combined with the target due to the conformational alteration of the aptamer structure, resulting in an increased fluorescence signal readout. Thrombin was sensitively determined as low as 1.6 nM in the range of 1.6–8.0 nM with a high selectivity. Finally, this sensor succeeded in detecting thrombin in a real fetal bovine serum.

Electrochemical sandwich-type thrombin aptasensor based on dual signal amplification strategy of silver nanowires and hollow Au–CeO2

Signal amplification is crucial in electrochemical biosensor to obtain low detection limits. In this work, a highly sensitive sandwich-type thrombin aptasensor is constructed, based on dual signal amplification of uniform silver nanowires (AgNWs) and hollow Au–CeO2 nanocomposites. AgNWs are decorated on the ITO surface to immobilize amino functionalized thrombin capture apemeter 1 (Apt1). And Au nanoparticles (AuNPs) grown directly on the surface of hollow CeO2 microstructure are used to immobilize sulfydryl functionalized thrombin reporter apemeter 2 (Apt2). Thus, sandwich-type apatasensor has been successfully designed, due to the specific recognition between thrombin and the two kinds of aptamers. One of the signal amplifications is from the good conductivity of uniform AgNWs. Moreover, uniform AgNWs together with hollow Au–CeO2 exhibit the good catalytic performance for the reduction of H2O2, further resulting in significant electrochemical signal amplification. Because the electrochemical signal amplification is closely related to the thrombin concentration, differential pulse voltammetry is used to specifically detect thrombin. Under the optimized conditions, the proposed method has a good linear response ranged from 0.5 pM to 30 nM with a low detection limit of 0.25 pM (S/N = 3) for thrombin. The proposed thrombin aptasensor displays good selectivity, reproducibility and stability, providing a good platform for the ultrasensitive detection of thrombin.

Electrochemical thrombin aptasensor based on using magnetic nanoparticles and porous carbon prepared by carbonization of a zinc(II)-2-methylimidazole metal-organic framework.

A homogeneous electrochemical aptasensor was obtained by modifying a glassy carbon electrode (GCE) with a porous carbon nanomaterial (Z-1000, about 70nm, deteced by transmission electron microscopic) that was obtained by carbonization of a zinc(II)-2-methylimidazole metal-organic framework. Z-1000 possesses a large specific surface and outstanding electrochemical properties. A thrombin-binding aptamer (CP) was immobilized on the magnetite nanoparticles MNPs by the condensation reaction and further combined with reporter probe (RP) that is functionalized with electroactive methylene blue (MB). In the presence of thrombin, the CP was specifically recognized with it to formthe CP/MNP/Thb complex, and the RP was dissociated from MNPs. The released RP was captured by the modified GCE through π-stacking interaction between nucleobases and carbon nanostructure. The electrical signal generatedby MB can be monitored by differential pulse voltammetry (DPV). Under the optimized conditions, the DPV peak current at around -0.28V (vs.SCE) increases with thrombin concentration. The sensor has a detection limit of 0.8 fM of thrombin and a linear range that extends from 10 fM to 100nM. It was successfully applied to the analysis of spiked serum. The recoveries are 98.1-99.4% and RSDs are 3.9%-4.0%. Conceivably, this aptasensor schemecan be easily extended to other proteins and gives inspiration to manufacture sensitive aptasensor. Graphical abstract A homogeneous electrochemical aptasensor is obtained by modifying a glassy carbon electrode with the MOF-derived porous carbon. The sensor has a detection limit of 0.8 fM and a wide linear range from 10 fM to 100nM for thrombin detection.

Hydrogel based aptasensor for thrombin sensing by Resonance Rayleigh Scattering

In this research, a novel Resonance Rayleigh Scattering (RRS) aptasensor was developed for thrombin monitoring using in-situ synthesized and embedded Au nanoparticles (AuNPs) into poly vinyl alcohol –borax hydrogel (PBH). Thiolated-thrombin binding aptamer (thiolated-TBA) was attached to the surface of AuNPs embedded into PBH to design the PBH-aptasensor for thrombin detection (thiolated-TBA@AuNPs–PBH). To verify the characteristic and morphology of PBH nanocomposite, energy dispersive X-ray analysis, TEM, average particle size analizer and UV–Vis spectra were performed. The difference in RRS intensities in the absence and presence of thrombin was calculated and selected as the monitoring signal. Effect of different parameters on the RRS signal was investigated at excitation wavelength of 500 nm. Under the approved conditions, the linear detection range was validated over the concentration of 0.70 pM- 0.02 μM. The limit of detection based on 3Sb was 0.10 pM. The relative standard deviation for 5.6 pM and 3.6 nM were 4.0 and 2.7% (n = 10), respectively. The proposed aptasensor was successfully applied as an experimental model for thrombin detection in serum samples of healthy volunteers with acceptable results.

Label-free and reagentless capacitive aptasensor for thrombin

This investigation develops a label-free and reagentless aptasensor, based on a capacitive transducer with simple face-to-face electrode pairs. The electrode pairs of the transducer are composed of a gold electrode and an indium tin oxide film with micrometer separation with a double-side polyethylene terephthalate tape. Aptamers and 1-dodecanethiol are modified to form a self-assembled monolayer (SAM) on the gold electrode surfaces, and function as bio-recognition elements and preventers of non-specific protein binding, respectively. Electrochemical characterization results indicate that the SAM also forms an effective insulating layer, which is sufficient for capacitive sensing. The feasibility of the capacitive biosensor is validated using thrombin as a model analyte. The ultra-small value changes of capacitance originating from thrombin binding with the aptamers modified on the biosensor were measured with a home-made capacitance measuring circuit based on switched capacitor (SC) technology. The developed biosensor has detection limits of 1 pM and 10 pM of thrombin in phosphate buffered saline and mimic serum solution, respectively. The linear range for thrombin detection in human serum solution is from 10 pM to 1 μM, with a regression coefficient of 0.98. Additionally, the proposed aptasensor does not have significant levels of non-specific binding of bovine serum albumin and human serum albumin. Accordingly, the combination of SC and SAM bringing capacitive transduction at the forefront of ultrasensitive label-free and reagentless biosensing devices, particularly for point-of-care clinical analysis, which adopts small numbers of biological samples with low analyte concentrations.

A feasibility study of a leaky waveguide aptasensor for thrombin.

This proof-of-principle study demonstrates the feasibility of a leaky waveguide (LW) aptasensor, where aptamers were immobilised in a mesoporous chitosan waveguiding film for the detection of thrombin. This work has demonstrated that aptamers immobilised in hydrogels retain their affinity and selectivity towards their target and thus can be used as bioreceptors. The use of antibodies as bioreceptors for sensing thrombin is not viable because it is a serine protease, which will cleave the antibodies. Currently used assays based on clotting time and chromogenic/fluorogenic substrates have limited potential for thrombin measurement in whole blood. Using the initial binding rate over the first 5 min, the limit of detection of our LW aptasensor for thrombin was ∼22 nM. The sensor was tested with spiked serum samples, giving a reading of 46.1 ± 4.6 nM for a sample containing 50 nM thrombin. Our proposed sensor combines the robustness and low cost of aptamers as molecular recognition elements with the simple fabrication process of the chitosan-based leaky waveguide, making LW aptasensors highly attractive for applications in point-of-care diagnostics and healthcare monitoring.

Electrochemiluminescent aptasensor for thrombin using nitrogen-doped graphene quantum dots.

An electrochemiluminescent (ECL) aptamer based method is described for the determination of thrombin. Three-dimensional nitrogen-doped graphene oxide (3D-NGO) was placed on a glassy carbon electrode (GCE) to provide an electrode surface that displays excellent electrical conductivity and acts as a strong emitter of ECL. The modified electrode was further coated with chitosan via electrodeposition. Finally, the amino-modified aptamer was immobilized on the modified GCE. The interaction between thrombin and aptamer results in a decrease in ECL. The assay has a linear response in the 1 fM to 1nM thrombin concentration range and a 0.25 fM lower detection limit (at an S/N ratio of 3). The method was applied to the determination of thrombin in spiked human plasma samples, and recoveries ranged between 94 and 105% (with RSDs of <3.6%).The calibration plot was recorded at potential and wavelength of fluorescence emission (wavelength: 445nm; potential: 0 to -2V). Graphical abstract A bare glassy carbon electrode (GCE) does not display electrochemiluminescence (ECL). If, however, nitrogen-doped graphene quantum dots,chitosan, andthree-dimensional nitrogen-doped graphene oxide (NGQD-chitosan/3D-NGO) are electrodeposited on the GCE, strongECL can be observed. The ECL intensity decreased after aptamer and bovine serum albumin (BSA) were dropped onto the electrode (curve a). However, the ECL further decreases after addition of thrombin (TB;curve b).