A sensitive sandwich-type electrochemical aptasensor for thrombin detection based on platinum nanoparticles decorated carbon nanocages as signal labels

Single-atom nanozymes: Emerging talent for sensitive detection of heavy metals

In recent years, the increasingly severe pollution of heavy metals has posed a significant threat to the environment and human safety. Heavy metal ions are highly non-biodegradable, with a tendency to accumulate through biomagnification. Consequently, accurate detection of heavy metal ions is of paramount importance. As a new type of synthetic nanomaterials, single-atom nanozymes (SANs) boast exceptional enzyme-like properties, setting them apart from natural enzymes. This unique feature affords SANs with a multitude of advantages such as dispersed active sites, low cost and variety of synthetic methods over natural enzymes, making them an enticing prospect for various applications in industrial, medical and biological fields. In this paper, we systematically summarize the synthetic methods and catalytic mechanisms of SANs. We also briefly review the analytical methods for heavy metal ions and present an overall overview of the research progress in recent years on the application of SANs in the detection of environmental heavy metal ions. Eventually, we propose the existing challenges and provide a vision for the future.

Sandwich-type aptamer-based biosensors for thrombin detection

Thrombin, a proteolytic enzyme, plays an essential role in catalyzing many blood clotting reactions. Thrombin can act as a marker for some blood-related diseases, such as leukemia, thrombosis, Alzheimer's disease and liver disease. Therefore, its diagnosis is of great importance in the fields of biological and medical research. Biosensors containing sandwich-type structures have attracted much consideration owing to their superior features such as reproducible and stable responses with easy improvement in the sensitivity of detection. Sandwich-type platforms can be designed using a pair of receptors that are able to bind to diverse locations of the same target. Herein, we investigate recent advances in the progress and applications of thrombin aptasensors containing a sandwich-type structure, in which two thrombin-binding aptamers (TBAs) identify different parts of the thrombin molecule, leading to the formation of a sandwich structure and ultimately signal detection. We also discuss the pros and cons of these approaches and outline the most logical approach in each section.

Biomedical,clinical and environmental applications of platinum-based nanohybrids: An updated review

Platinum nanoparticles (Pt NPs) have numerous applications in various sectors, including pharmacology, nanomedicine, cancer therapy, radiotherapy, biotechnology and environment mitigation like removal of toxic metals from wastewater, photocatalytic degradation of toxic compounds, adsorption, and water splitting. The multifaceted applications of Pt NPs because of their ultra-fine structures, large surface area, tuned porosity, coordination-binding, and excellent physiochemical properties. The various types of nanohybrids (NHs) of Pt NPs can be fabricated by doping with different metal/metal oxide/polymer-based materials. There are several methods to synthesize platinum-based NHs, but biological processes are admirable because of green, economical, sustainable, and non-toxic. Due to the robust physicochemical and biological characteristics of platinum NPs, they are widely employed as nanocatalyst, antioxidant, antipathogenic, and anticancer agents. Indeed, Pt-based NHs are the subject of keen interest and substantial research area for biomedical and clinical applications. Hence, this review systematically studies antimicrobial, biological, and environmental applications of platinum and platinum-based NHs, predominantly for treating cancer and photo-thermal therapy. Applications of Pt NPs in nanomedicine and nano-diagnosis are also highlighted. Pt NPs-related nanotoxicity and the potential and opportunity for future nano-therapeutics based on Pt NPs are also discussed.

In-Situ Fabrication of Electroactive Cu2+-Trithiocyanate Complex and Its Application for Label-Free Electrochemical Aptasensing of Thrombin

The preparation of an electroactive matrix for the immobilization of the bioprobe shows great promise to construct the label-free biosensors. Herein, the electroactive metal-organic coordination polymer has been in-situ prepared by pre-assembly of a layer of trithiocynate (TCY) on a gold electrode (AuE) through Au-S bond, followed by repetitive soaking in Cu(NO₃)₂ solution and TCY solutions. Then the gold nanoparticles (AuNPs) and the thiolated thrombin aptamers were successively assembled on the electrode surface, and thus the electrochemical electroactive aptasensing layer for thrombin was achieved. The preparation process of the biosensor was characterized by an atomic force microscope (AFM), attenuated total reflection-Fourier transform infrared (ATR-FTIR), and electrochemical methods. Electrochemical sensing assays showed that the formation of the aptamer-thrombin complex changed the microenvironment and the electro-conductivity of the electrode interface, causing the electrochemical signal suppression of the TCY-Cu²⁺ polymer. Additionally, the target thrombin can be label-free analyzed. Under optimal conditions, the aptasensor can detect thrombin in the concentration range from 1.0 fM to 1.0 μM, with a detection limit of 0.26 fM. The spiked recovery assay showed that the recovery of the thrombin in human serum samples was 97.2-103%, showing that the biosensor is feasible for biomolecule analysis in a complex sample.

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.

Recent trends in nanomaterial-based signal amplification in electrochemical aptasensors

Ultrasensitive biosensors have become a necessity in the world of scientific research, and several signal enhancement strategies have been employed to attain exceptionally low detection limits. Nanotechnology turns out to be a strong contender for signal amplification, as they can be employed as platform modifiers, catalysts, carriers or labels. Here, we have described the most recent advancements in the utilization of nanomaterials as signal amplification components in aptamer-based electrochemical biosensors. We have briefly reviewed the methods that utilized nanomaterials, namely gold and carbon, as well as nanocomposites such as: graphene, carbon nanotubes, quantum dots, and metal-organic frameworks.

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.

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.

Efficient immobilization of aptamers on the layered double hydroxide nanohybrids for the electrochemical proteins detection

Despite the use of layered double hydroxides (LDH) in different electrochemical (bio)sensors, the construction of aptasensors using LDH-based surfaces was not reported to the best of our knowledge. This may be due to the lack of a suitable linker to attach aptamers to the LDH-modified surface. LDH-based aptasensors are established here as very sensitive and reliable devices in serum and cerebrospinal fluid (CSF) analysis. 5'-NH₂ DNA aptamer probes were immobilized on the LDH-based surfaces in a vertical conformation without any linker materials. Due to the low electron conductivity of the LDH, carbon nanotubes (CNT) with high electronic conductivity and high surface area were combined with LDH. Thrombin was used as a model protein for aptasensing. The sensor shows a linear range of 0.005-12,000 pmol L^-1 and a limit of detection of 0.1 fmol L^-1. Moreover, the aptasensor was used for the sensing of thrombin in CSF and serum samples acquired from both healthy and patients with different disease.

Highly sensitive host-guest mode homogenous electrochemical thrombin signal amplification aptasensor based on tetraferrocene label

The development of sensitive and convenient detection methods to monitor thrombin without the use of enzymes or complex nanomaterials is highly desirable for the diagnosis of cardiovascular diseases. In this article, tetraferrocene was first synthesized and then a sensitive and homogeneous electrochemical aptasensor was developed for thrombin detection based on host-guest recognition between tetraferrocene and β-cyclodextrin (β-CD). In the absence of thrombin, the double stem-loop of thrombin aptamer (TBA) prevented tetraferrocenes labeled at both ends from entering the cavity of β-CD deposited on gold electrode surface. After binding with thrombin, the stem-loop structure of TBA opened and transformed into special G-quarter structure, forcing tetraferrocene into the cavity of β-CD. As a result, thrombin allowed eight ferrocene molecules to reach the gold electrode surface, greatly amplifying the response signal. The obtained aptasensors showed dynamic detection range from 4 pM to 12.5 nM with detection limit around 1.2 pM. Overall, the results indicate that the proposed aptasensors are promising for future rapid clinical detection of thrombin and development of signal amplification strategies for detection of various proteins.

A sensitive homogenous aptasensor based on tetraferrocene labeling for thrombin detection

In this work, a novel homogeneous electrochemical aptasensor based on electrically assisted bond and tetraferrocene signal amplification was constructed for thrombin detection. Importantly, modification of the electrode is not necessary for this sensor, requiring only the construction of a simple and efficient probe. In addition, a brand new signal marker-tetraferrocene, containing four ferrocene molecules, was employed as a label to the terminal position of the probe. Compared with a single ferrocene moiety, tetraferrocene possesses a larger amplification signal for rapid detection of thrombin. In the detection of thrombin, the selected aptamer probe with a stem-loop structure was labeled with tetraferrocene at the 3' terminal and thiol at the 5' terminal, respectively. Confinement of the thiol to the stem-loop structure of the probe, the ability of thiol to reach the surface of electrode lossed even with the aid of the applied potential. However, upon treatment with the target protein of thrombin the stem-loop structure opened, promoting rapid attachment of the thiol group to the electrode interface generating Au-S self-assembly with the action of potential-assistance. The electrochemical signal of tetraferrocene could be measured by differential pulse voltammetry (DPV), which was subsequently used for target quantitative detection. This strategy displayed a detection limit as low as 0.126 pM, and an inherently high specificity for the detection of a single mismatch. Moreover, it exhibited advanced specificity against common interfering proteins.

Label-free electrochemical aptasensor for progesterone detection in biological fluids

A label-free electrochemical progesterone (P4) aptasensor was successfully developed by covalently immobilizing NH₂-functionalized P4-specific aptamer on the electrode surface. The NiO-Au hybrid nanofibers were synthesized by the electrospinning technique. GQDs-NiO-AuNFs nanocomposite was prepared by dispersing of electrospun NiO-AuNFs in the as-synthesized graphene quantum dots (GQDs) solution and stirring for 24 h. Novel GQDs-NiO-AuNFs nano-architecture in combination with functionalized multiwalled carbon nanotubes (f-MWCNTs) were further utilized to modify screen printed carbon electrode (SPCE) in order to construct an effective immobilization matrix with plenty of carboxylic functional groups. The stepwise assembly process of the designed aptasensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The aptamer-progesterone complex formation led to a hindered electron transfer reaction on the sensing interface, which decreased the redox probe peak current. Based on of this, progesterone could be quantitatively detected by monitoring the decrease of differential pulse voltammetric (DPV) responses of [Fe(CN)₆]^3-/4- peak current with increasing the progesterone concentration. Under optimized experimental parameters, the aptasensor exhibited a dynamic concentration range from 0.01 to 1000 nM and a detection limit of 1.86 pM. The proposed aptasensor was successfully employed for the determination of progesterone in human serum samples and pharmaceutical formulations.

The synergistic effect of Au-COF nanosheets and artificial peroxidase Au@ZIF-8(NiPd) rhombic dodecahedra for signal amplification for biomarker detection

Here, a new type of signal amplification strategy is proposed employing Au nanoparticle (AuNP)-functionalized covalent organic framework (Au-COF) nanosheets and AuNP functionalized ZIF-8(NiPd) (Au@ZIF-8(NiPd)) rhombic dodecahedra nanocomposites for sandwich electrochemical sensor construction. The peroxidase mimics Au@ZIF-8(NiPd) took the place of natural enzymes in enzyme-assisted amplification strategies, both acting as catalysts for H₂O₂ reduction for signal amplification, and serving as ideal nanocarriers for signal probe anchoring. The cancer biomarker thrombin (TB) was selected as the target. Thrombin binding aptamers (TBA 2) were fixed on Au@ZIF-8(NiPd), and the obtained TBA 2-Au@ZIF-8(NiPd) bioconjugates were employed as tracer labels, and TB was sandwiched between the tracer labels and capture probe TBA 1 which were immobilized on the Au-COF nanosheet modified electrode. Au-COFs with a high specific area, super electroconductivity, and uniformly distributed AuNPs were utilized as the electrode substrate to fix TBA 1. Exploiting the sandwich method, the proposed TB aptasensor exhibited a wide linear range of 0.1 pM to 20 nM with a low detection limit of 15 fM (S/N = 3). The ingenious sensing strategy enriched the application diversity of the artificial enzyme and showed promise in research and development of point-of-care diagnostics.

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.

Rapid and sensitive detection of nodularin-R in water by a label-free BLI aptasensor

Contamination of freshwater with nodularin-R (NOD-R) represents a significant global environmental and public health concern. However, ethical problems and technical difficulties surrounding the current detection methods for NOD-R necessitate further studies to devise appropriate alternatives within a regulatory monitoring regime. In this work, we employed an aptamer as a specific recognition element and developed a biolayer interferometry (BLI) biosensor platform for NOD-R detection. The aptasensor we propose displayed a broad detection range from 40 to 600 nM NOD-R (and a linear response range from 40 to 200 nM), and achieved a detection limit as low as 167 pM. In addition, the aptamer-based biosensor was shown to possess high selectivity, as well as good reproducibility and stability. We believe that this novel aptamer-based biosensor provides a potential alternative for the sensitive and rapid detection of NOD-R.

Trimetallic signal amplification aptasensor for TSP-1 detection based on Ce-MOF@Au and AuPtRu nanocomposites

In this work, an aptamer was used as the target capturing agent and a trimetallic signal amplification strategy based on Ce-MOF@Au and AuPtRu NPs was demonstrated for the sensitive detection of TSP-1. Herein, the synthesized AuPtRu nanocomposite (AuPtRu NPs) not only acts as the catalyst for catalyzing hydrogen peroxide but also acts as a nanocarrier for capturing the -NH₂ termination single strand DNA (S1) to obtain the signal probe (SP, AuPtRu nanocomposite/S1). Then, SP was efficiently linked into TSP-1 aptamers with the addition of complementary linking strands to form M1 (SP/aptamer). The Ce-MOF@Au nanocomposites were obtained by in situ reduction and used as GCE electrode modification materials. The -NH₂-modified capture probe (CP) DNA was immobilized on the surface of Ce-MOF@Au nanocomposites for hybridizing SP. In the presence of the target TSP-1, the aptamer recognizes the target and binds strongly so that SP is released from the prepared M1 and then hybridized with CP. When the detection solution contains an electrochemical matrix of H₂O₂, AuPtRu NPs can oxidize H₂O₂ to obtain an enhanced signal. Furthermore, the proposed aptasensor has a very low LOD of 0.13 fg mL^-1 TSP-1 in the detection range of 1 fg mL^-1 to 10 ng mL^-1. Moreover, the proposed platform also has application implications for other potential targets.

2D-porphrinic covalent organic framework-based aptasensor with enhanced photoelectrochemical response for the detection of C-reactive protein

In this study, a novel photoelectrochemical (PEC) aptasensor based on two-dimensional (2D) porphyrinic covalent organic frameworks (p-COFs) for the label-free detection of C-reactive protein (CRP) is presented. The obtained p-COFs possess high conductivity and an improved stability due to strong and rigid covalent linkages. The introduction of p-COFs hinder the recombination of electrons and holes, decreasing their band gap (E_g), thereby which improved the photocurrent conversion efficiency. Compared with pure porphyrin, p-COFs exhibited enhanced photocurrent intensity. An amplified photocurrent conversion efficiency and enhanced photocurrent results from H₂O₂, which act as active molecules and electron donors. As an unprecedented application of COFs in PEC bioanalysis, the detection of CRP with a PEC aptasensor is presented. The assembly of a CRP aptamer on the surface of Ag nanoparticles hinders the electron transfer, resulting in the decrease of the photocurrent response. This PEC aptasensor exhibits good analytical performances such as a rapid response, high stability, wide linear range and excellent selectivity, making COFs promising candidates for PEC bioanalysis.

A versatile label-free electrochemical biosensor for circulating tumor DNA based on dual enzyme assisted multiple amplification strategy

A versatile label-free electrochemical biosensor based on dual enzyme assisted multiple amplification strategy was developed for ultrasensitive detection of circulating tumor DNA (ctDNA). The biosensor consists of a triple-helix molecular switch (THMS) as molecular recognition and signal transduction probe, ribonuclease HII (RNase HII) and terminal deoxynucleotidyl transferase (TdT) as dual enzyme assisted multiple amplification accelerator. The presence of target ctDNA could open THMS and trigger RNase HII-assisted homogenous target recycling amplification to produce substantial signal transduction probe (STP). The released STP hybridized with the capture probe immobilized on a gold electrode, then TdT and assistant probe were further employed to fulfill TdT-mediated cascade extension and generate stable DNA dendritic nanostructures. The electroactive methyl blue (MB) was finally used as the signal reporter to realize the multiple electrochemical amplification ctDNA detection as the amount of MB is positively correlated with the target ctDNA. Combined with the efficient recognition capacity of the designed THMS and the excellent multiple amplification ability of RNase HII and TdT, the constructed sensing platform could detect KRAS G12DM with a wide detection range from 0.01 fM to 1 pM, and the limit of detection as low as 2.4 aM. Besides, the platform is capable of detecting ctDNA in biological fluid such as plasma. More importantly, by substituting the loop of THMS with different sequences, this strategy could be conveniently expanded into the detection of other ctDNA, showing promising potential applications in clinical cancer screening and prognosis.

Magnetic force assisted electrochemical sensor for the detection of thrombin with aptamer-antibody sandwich formation

A magnetic force assisted electrochemical aptamer-antibody sandwich assay (MESA) was developed for the detection of thrombin as a model protein in serum samples. The MESA using the formation of sandwich complexes on the electrochemical sensor probe for reaction and the removal of unbound bioconjugates from the sensor surface without washing are controlled by a magnetic field. Thrombin was determined by the cathodic currents of a toluidine blue O (TBO) attached with thrombin antibody modified magnetic nanoparticle (MNP) at the sensor surface. To detect thrombin in a serum sample, we applied a thrombin-specific aptamer as the capture molecule bound to the functionalized conducting polymer layer (poly-(2,2´:5´,5″-terthiophene-3´-p-benzoic acid) (pTBA)), and streptavidin and starch coated-MNP was conjugated with biotinylated thrombin antibodies (Ab) and TBO as the bioconjugate (MNP@Ab-TBO). The characterization of MNP@Ab-TBO and sensor probe was performed using voltammetry, impedance spectroscopy, XPS, and UV-VIS spectroscopy. The experimental conditions were optimized in terms of pH, binding time, removal time of unbound bioconjugates, and applied potential. The dynamic ranges of thrombin were from 1.0 to 500 nM with detection limit of 0.49 ( ± 0.06) nM. The recovery test demonstrates the reliability of the proposed sensing system for a handheld device.

The aptamer-thrombin-aptamer sandwich complex-bridged gold nanoparticle oligomers for high-precision profiling of thrombin by dark field microscopy

We present a simple and efficient colorimetric assay strategy for ultrasensitive visual detection of human α-thrombin, which is essentially based on the formation of the DNA1-thrombin-DNA2 sandwich complex-bridged gold nanoparticle (Au NP) oligomers. Unlike the traditional colorimetric sensing strategies which induced the nanoparticle aggregates with uncontrolled aggregate size. In this work, the DNA1with rich G bases was firstly conjugated on the surfaces of Au NPs fixed on the hexadecyl trimethylammonium bromide (CTAB)-coated glass slide, and thrombin was captured by the DNA1. Then, the other DNA2 with rich G bases interacted with the former DNA1-thrombin complex and formed a DNA1-thrombin-DNA2 sandwich complex. The subsequently added Au NPs can be bound to the Au NP-DNA1-thrombin-DNA2 via Au-S bond to trigger the formation of Au NP oligomers, an apparent color change of the single Au NPs from green to yellow and red was observed under dark field microscopy. By measuring the intensity change of the yellow and red Au NPs, the concentration of target thrombin could be accurately quantified. As a proof of concept experiment, the formation of Au NP oligomers resulted in significantly improved sensitivity (10 fM of limit of detection and 20 fM of limit of quantity) and wider linear dynamic range of thrombin detection (20 fM-20 nM), the relative standard deviation (RSD) was less than 5.73% (n = 5). In addition, in order to validate the potential application in clinical diagnosis, the content of thrombin in a human serum samples was also quantified.

Platinum nanoparticles in nanobiomedicine

Oxidative stress-dependent inflammatory diseases represent a major concern for the population's health worldwide. Biocompatible nanomaterials with enzymatic properties could play a crucial role in the treatment of such pathologies. In this respect, platinum nanoparticles (PtNPs) are promising candidates, showing remarkable catalytic activity, able to reduce the intracellular reactive oxygen species (ROS) levels and impair the downstream pathways leading to inflammation. This review reports a critical overview of the growing evidence revealing the anti-inflammatory ability of PtNPs and their potential applications in nanomedicine. It provides a detailed description of the wide variety of synthetic methods recently developed, with particular attention to the aspects influencing biocompatibility. Special attention has been paid to the studies describing the toxicological profile of PtNPs with an attempt to draw critical conclusions. The emerging picture suggests that the material per se is not causing cytotoxicity, while other physicochemical features related to the synthesis and surface functionalization may play a crucial role in determining the observed impairment of cellular functions. The enzymatic activity of PtNPs is also summarized, analyzing their action against ROS produced by pathological conditions within the cells. In particular, we extensively discuss the potential of these properties in nanomedicine to down-regulate inflammatory pathways or to be employed as diagnostic tools with colorimetric readout. A brief overview of other biomedical applications of nanoplatinum is also presented.

Ratiometric electrochemical aptasensor based on ferrocene and carbon nanofibers for highly specific detection of tetracycline residues

A sensitive and efficient ratiometric electrochemical aptasensor was designed for tetracycline (TET) detection in milk. The ratiometric electrochemical aptasensor was constructed by integrating two aptasensors termed as aptasensor 1 and aptasensor 2. The aptasensor 1 was fabricated that based on ferrocene (Fc) and gold nanoparticles (AuNPs) nanocomposite. Meanwhile, the aptasensor 2 was prepared that based on carbon nanofibers (CNFs) and AuNPs nanocomposite. TET-aptamer was immobilized effectively onto screen-printed carbon electrodes (SPCEs) surface through forming Au-S bond between AuNPs and thiol of aptamer at 5′ end to construct the aptasensor 1 and aptasensor 2. And their detection results were calculated by ratio. Thus, the proposed ratiometric aptasensor solved the problem of low accuracy and large differences between batches. Under the optimized conditions, the TET was detected by differential pulse voltammetry (DPV). Taken advantage of ratio calculation, the as-prepared ratiometric aptasensor could detect TET quantitatively in the range of 10⁻⁸–10⁻³gL⁻¹, with a detection limit of 3.3 × 10⁻⁷gL⁻¹. Moreover, its applicability to TET-contaminated real samples (milk) showed an excellent agreement with the values determined by ultrahigh-performance liquid chromatography-tandem mass spectrometry (UPLC-ESI-MS/MS). With high sensitivity, accuracy and reliability, the developed ratiometric aptasensor held a great potential in TET detection for food safety.

Synthesis of a multi-functional DNA nanosphere barcode system for direct cell detection

Nucleic acid-based technologies have been applied to numerous biomedical applications. As a novel material for target detection, DNA has been used to construct a barcode system with a range of structures. This paper reports multi-functionalized DNA nanospheres (DNANSs) by rolling circle amplification (RCA) with several functionalized nucleotides. DNANSs with a barcode system were designed to exhibit fluorescence for coding enhanced signals and contain biotin for more functionalities, including targeting through the biotin-streptavidin (biotin-STA) interaction. Functionalized deoxynucleotide triphosphates (dNTPs) were mixed in the RCA process and functional moieties can be expressed on the DNANSs. The anti-epidermal growth factor receptor antibodies (anti-EGFR Abs) can be conjugated on DNANSs for targeting cancer cells specifically. As a proof of concept, the potential of the multi-functional DNANS barcode was demonstrated by direct cell detection as a simple detection method. The DNANS barcode provides a new route for the simple and rapid selective recognition of cancer cells.

Dendrimer-like amino-functionalized hierarchical porous silica nanoparticle: A host material for 2,4-dichlorophenoxyacetic acid imprinting and sensing

In this work, a novel molecularly imprinted electrochemical sensor based on the amino-functionalized silica nanoparticles was built for the sensitive and selective detection of 2,4-dichlorophenoxyacetic acid (2,4-D). The hierarchical porous dendrimer-like silica nanoparticles (HPSNs-NH₂) were synthesized by an ethyl ether emulsion method. The selective molecularly imprinted polymers (MIP) was prepared on the HPSNs-NH₂ modified electrode via electropolymerization by using 2,4-D as the template and o-phenylenediamine (OPD) as the monomer. The porous structure of HPSNs-NH₂ reduced the diffusion limitations of the analytes, enhanced the accessibility and increased the surface area of the sensor, while the MIP layer offered the ability to recognize and quantify target 2,4-D by using ferro/ferricyanide as probes. Several significant experimental parameters on the analytical performance of the MIP/HPSNs-NH₂ sensor were explored and optimized. Under the optimized condition, the sensor displayed an appreciable selectivity over structurally related compounds and good sensitivity toward 2,4-D. The linear range of 2,4-D detection was from 1.00 × 10^-10 to 2.50 × 10^-8M and the detection limit was down to 1.17 × 10^-11M according to the 3S_a/b criteria. This method has been applied to detect 2,4-D in bean sprout samples with satisfying results.

Competition-derived FRET-switching cationic conjugated polymer-Ir(III) complex probe for thrombin detection

A novel, label-free and convenient strategy for thrombin assay has been developed based on the fluorescence resonance energy transfer (FRET) from a cationic conjugated polymer (CCP) to Ir(III) complex. The energy donor (CCP) and acceptor (Ir(III) complex) were taken into close proximity through π-π stacking interaction and electrostatic interaction, leading to the occurrence of FRET. However, the introduction of the thrombin aptamer upset the status and blocked the FRET process, but afterwards the reappearance of FRET phenomenon was confirmed by the special binding interaction between aptamer and thrombin, thus achieving the quantitative detection of thrombin. This assay could detect thrombin as low concentration as about 0.05pM and provided a highly specific selectivity among other nonspecific proteins. Moreover, the strategy may allow our platform to provide similar sensitivity toward different targets in an aptamer-structure-independent manner. Furthermore, the assay can be used to detect thrombin in diluted real urine or serum samples with a satisfactory recovery, implying its great potential for rapid detection of thrombin in the clinic.

Electrochemical aptasensor for thrombin using co-catalysis of hemin/G-quadruplex DNAzyme and octahedral Cu2O-Au nanocomposites for signal amplification

In this work, novel octahedral Cu₂O-Au nanocomposites were synthesized and first applied in an electrochemical aptasensor to detect thrombin (TB) with the aid of a DNAzyme for signal amplification. The octahedral Cu₂O-Au nanocomposites have not only simultaneously served as signal amplifying molecules but have also been utilized as an ideal loading platform to immobilize a large number of electroactive substances and recognition probes. Gold nanoparticles (AuNPs) were grown directly on the surface of the octahedral Cu₂O nanocrystals, and the Cu₂O-Au nanocomposites obtained had the advantages of large surface areas and excellent biocompatibilities. The hemin/G-quadruplex, which was formed by intercalating hemin into the amino terminated thrombin binding aptamer (NH₂-TBA), and the electroactive toluidine blue (Tb) were immobilized onto the Cu₂O-Au nanocomposite surfaces through a stable Au-N bond. AuNPs, Cu₂O and hemin/G-quadruplex co-catalyse the H₂O₂ in the working buffer to promote the electron transfer of Tb as a multiple signal amplification strategy in order to improve the performance of the electrochemical aptasensor. Under optimal conditions, the designed aptasensor exhibited sensitive detection of TB from 100 fM to 20nM with a lower detection limit of 23fM. This proposed aptasensor exhibited good sensitivity, high specificity and acceptable reproducibility and could be widely applied in bioassay analysis.

Flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblast cancer cells using MWCNTs-Pdnano/PTCA/aptamer as labeled aptamer for the signal amplification

In this research, we demonstrated a flow injection amperometric sandwich-type aptasensor for the determination of human leukemic lymphoblasts (CCRF-CEM) based on poly(3,4-ethylenedioxythiophene) decorated with gold nanoparticles (PEDOT-Au_nano) as a nano platform to immobilize thiolated sgc8c aptamer and multiwall carbon nanotubes decorated with palladium nanoparticles/3,4,9,10-perylene tetracarboxylic acid (MWCNTs-Pd_nano/PTCA) to fabricate catalytic labeled aptamer. In the proposed sensing strategy, the CCRF-CEM cancer cells were sandwiched between immobilized sgc8c aptamer on PEDOT-Au_nano modified surface electrode and catalytic labeled sgc8c aptamer (MWCNTs-Pd_nano/PTCA/aptamer). After that, the concentration of CCRF-CEM cancer cells was determined in presence of 0.1 mM hydrogen peroxide (H₂O₂) as an electroactive component. The attached MWCNTs-Pd_nano nanocomposites to CCRF-CEM cancer cells amplified the electrocatalytic reduction of H₂O₂ and improved the sensitivity of the sensor to CCRF-CEM cancer cells. The MWCNT-Pd_nano nanocomposite was characterized with transmission electron microscopy (TEM) and energy dispersive X-ray (EDX). The electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to confirm the stepwise changes in the electrochemical surface properties of the electrode. The proposed sandwich-type electrochemical aptasensor exhibited an excellent analytical performance for the detection of CCRF-CEM cancer cells ranging from 1.0 × 10¹ to 5.0 × 10⁵ cells mL^-1. The limit of detection was 8 cells mL^-1. The proposed aptasensor showed high selectivity toward CCRF-CEM cancer cells. The proposed aptasensor was also applied to the determination of CCRF-CEM cancer cells in human serum samples.

Molybdenum disulfide sphere-based electrochemical aptasensors for protein detection

In this work, we report the development of an ultrasensitive sandwich-type electrochemical aptasensor for protein detection.

An ultrasensitive chemiluminescence aptasensor for indirect hemin detection based on aptamer recognition materials

MGO@H-Atp@Co-PP polymers were successfully prepared and used to construct a MGO@H-Atp@Co-PP-CL aptasensor.