Fluorescent Aptasensor Research Articles

A fluorescence and colorimetric dual-mode aptasensor for kanamycin detection

A fluorescence and colorimetric dual-mode aptasensor for kanamycin detection

Detection of C-reactive protein using a label-free NIR fluorescent aptasensor with a large Stokes shift based on an AIEE anthracene derivative

BackgroundC-reactive protein (CRP), one of the classic biomarkers of inflammation, is closely related to infectious inflammation, cardiovascular disease, cancer, and other diseases. Therefore, timely and accurate detection of CRP in human blood is crucial for the discovery, diagnosis, and treatment of the aforementioned diseases. Herein, a novel label-free NIR fluorescence aptasensor with a large Stokes shift based on an AIEE anthracene derivative B and a molybdenum disulfide (MoS2) platform was developed and used for the high sensitivity and specificity detection of CRP. ResultsCompound B could emit near-infrared (NIR) fluorescence with a large Stokes shift (190 nm). Notably, this compound could bind with the aptamer of CRP (CRP-Apt) through electrostatic attraction to form a B/CRP-Apt complex, generating an aggregation-induced emission enhancement effect and enhancing the fluorescent intensity of B. B/CRP-Apt could be adsorbed on the surface of MoS2 with the addition of MoS2 to its solution, and the fluorescence of Compound B was quenched. CRP was then added to the above solution. CRP-Apt had a substantially higher affinity for CRP than MoS2. Therefore, B/CRP-Apt detached from the surface of MoS2 and bound to CRP, thereby restoring the fluorescence of B. Experimental results showed a good linear relationship between the fluorescent recovery intensity of B and the concentration of CRP in the concentration range of 0.3–70 ng mL−1, with a limit of detection as low as 0.1 ng mL−1. Significance and NoveltyThe aptasensor integrates the advantages of high sensitivity of NIR fluorescence, high specificity of aptamers, good water-solubility and AIEE effect of Compound B. And it could be applied to the determination of CRP in human serum samples, while most of the reported methods can only determine CRP in spiked human serum samples.

Simple solution and paper-based fluorescent aptasensors for toxic metal ions, thallium(l) and lead(ll).

Heavy metal ions, such as thallium(I) and lead(II) are environmental toxicants known to cause a severe threat to human and ecosystem health. This work investigates aptamers and intercalating chromophore-based complexes for the detection of these toxic species. In one method, a selective label-free "turn-on" biosensor was developed using a G-quadruplex-intercalating agent, berberine. Fluorescence, melting temperature (Tm), and circular dichroism analysis confirmed the affinity and selectivity results, illustrating the potential of these aptasensor methods for improving detection limits. These fluorescence assays were found to perform with a detection limit of 3.4 μM for Tl(I) and 0.84 nM for Pb(II). Furthermore, the assays were challenged successfully with Tl(I) and Pb(II) spiked into river water samples. We next developed paper-based fluorescent assays for Tl(I) and Pb(II), where the aptamer/berberine complex was spotted onto the paper test zone. When Tl(I) or Pb(II) ions solutions were spotted onto the top of the test zone and the spot was illuminated with a portable UV light (365 nm), a strong green fluorescence could be easily visualized with the naked eye. The lowest detection limits achieved with these fluorescent paper-based assays for Tl(I) and Pb(II) were 1.1 nM and 1.6 nM, respectively. The two fluorescent approaches presented here have the potential to be the basis of rapid, fast, and cost-efficient screening assays for these toxic species.

Dual-mode sensing platform for Bisphenol A detection via bifunctional CsPbBr3@Cu-MOF assisted fluorescence and colorimetric analysis

BackgroundBisphenol A (BPA) has been identified as an endocrine disruptor with numerous detrimental effects on human health. There is an urgent need to develop fluorescence/colorimetric dual-mode sensing approaches with expanded detection linear range, increased accuracy, and enhanced application flexibility for BPA detection. The utilization of fluorescence and colorimetric signals in point-of-care applications and real-time sensitive sensing further highlights the significance of developing novel and efficient fluorescence/colorimetric dual-mode sensing platform with high-efficiency probes. ResultsHerein, a fluorescence and colorimetric dual-mode aptasensor was developed by using CsPbBr3@Cu-MOF as the aptamer immobilization matrix and signal generator. CsPbBr3 was functionalized with Cu-MOF using a simple two-step strategy. This strategy involved in-situ formation and modified ligand-assisted precipitation technique with 4,4′-bipyridine (4,4-Bpy) serving as the bifunctional linker. The resulting CsPbBr3@Cu-MOF exhibited improved stability in water and enhanced fluorescence. Additionally, it functioned as peroxidase mimetic to oxidize 3,3′,5,5′-tetramethyl benzidine (TMB), leading to a colorimetric change from colorless to blue. In the presence of BPA, aptamers were removed from CsPbBr3@Cu-MOF. Consequently, the fluorescence and peroxidase-activity of CsPbBr3@Cu-MOF were recovered, resulting in the enhanced fluorescence intensity and color change of TMB. Using this system, the proposed aptasensor demonstrated detection ranges of 1.0–80.0 nM with a LOD of 0.60 nM for the colorimetric method, and a linearity range of 0.1–100 nM with a LOD of 0.02 nM for the fluorescence method. SignificanceThe obtained CsPbBr3@Cu-MOF composites showed excellent fluorescence properties, good peroxidase-like activity, and aqueous stability. Furthermore, the proposed dual-mode aptasensor demonstrated simplicity, cost-effectiveness and good anti-interference abilities. This can be extended to the construction of other dual-mode sensors by changing aptamers and provides novel insights on the potential applications of perovskites in bioanalysis.

A fluorescent platform integrated with a “one-pot” nicking endonuclease signal amplification and magnetic separation for simultaneous detection of tumor markers

Although Enzyme-linked immunosorbent assay (ELISA) has been widely used for biomedical research, simultaneous sensitive and cost-effective detection of multiple biomarkers is challenging. Herein, we proposed a “one-pot” nicking endonuclease signal amplification (NESA)-based fluorescent aptasensor for simultaneous detection of carcinoembryonic antigen (CEA) and alpha fetoprotein (AFP). Firstly, two aptamers were synchronously immobilized on the surface of magnetic nanoparticles (MNPs) by coupling with two complementary DNA (cDNA). CEA and AFP specifically recognized the aptamers and then the released cDNA (ssDNA) from the double-strands (dsDNA) triggers NESA, further breaking two detection probes which were labeled with the fluorescent dye (FAM and ROX) and its quencher (BHQ1 and BHQ2) at the same time. Then, the fluorescence signal of FAM and ROX were restored separately. The results indicated that the fluorescence intensity at the emission wavelength of 518 nm and 610 nm had a positive correlation with CEA and AFP concentrations, respectively. Under the optimum conditions, wider liner range of 1–500 ng mL−1 to CEA and 5–800 ng mL−1 to AFP of this fluorescent aptasensor were successfully obtained, achieving a detection limit of CEA and AFP were 0.7 ng mL−1 and 2 ng mL−1, respectively. Hence, it turned out that the aptasensor strategy can be a promising candidate for developing a newly fluorescence assay for the simultaneous quantitative detection of multiple tumor markers in matrix samples by changing the corresponding sequences of aptamer and fluorescent signal probe, which has great potential for the screening of early cancer.

Innovative fluorescent aptasensor for sensitive tropomyosin detection in shrimp products using DNA-templated silver nanoclusters and catalytic hairpin assembly

Innovative fluorescent aptasensor for sensitive tropomyosin detection in shrimp products using DNA-templated silver nanoclusters and catalytic hairpin assembly

Construction of fluorescent aptasensor based on graphene oxide for the detection of metronidazole in food

Aiming at the detection of metronidazole (MNZ) residues in food, a high sensitivity fluorescent aptasensor was designed, which carboxyfluorescein (FAM)-labeled nucleic acid aptamer (FAM-MNZ) as the core probe and graphene oxide (GO) as an efficient fluorescence quencher. The principle is that GO adsorbs the aptamer onto the surface, causing short-range contact between the fluorescent group of the aptamer and GO. Due to its sp2 hybridized domains, GO undergoes fluorescence resonance energy transfer (FRET). Thus, the fluorescence is quenched. When MNZ is added, it preferentially forms a stable complex with the aptamer without FRET. Under optimized conditions, milk samples can be accurately detected with a detection limit of 0.033 μM. In addition, molecular docking, lumo electron orbital simulations, and experimental methods were used to explore the effect of different average radial sizes of single-layer GO on sensing performance. It is shown that GO with a larger average size makes it easy for aptamers to be regularly arranged on its surface. This also provides a basis for electron transfer, resulting in higher fluorescence quenching ability through the FRET mechanism. Therefore, the constructed fluorescent aptamer sensor has a significant application value in food detection.

An autocatalytic hybridization circuit-based FRET aptasensor for detection of low-abundant sulfameter in human serum

Exposure to antibiotics is considered a potential risk factor for human health. Yet, the extensive and cost-effective detection of low-abundant antibiotics in complex matrices remains a significant challenge. Herein, an aptamer and an autocatalytic hybridization circuit (AHC) were used to fabricate a fluorescence resonance energy transfer (FRET) platform to detect sulfameter (SME) in human serum. The AHC system comprised two mutually motivated hybridization chain reactions (HCR) modules, ultimately producing long-branched DNA copolymeric nanowires. This mutually reciprocal activation of two HCR modules enables continuous signal amplification, providing the AHC system with wide linear range and high sensitivity for the SME detection. Compared to the HCR-based aptasensor, the AHC-based aptasensor exhibited a wider linear range and improved sensitivity (3.3 times greater). Under optimal conditions, the fluorescent AHC-based aptasensor demonstrated a linear range (R2 was 0.996) from 0.5 to 2000 nM, with a low detection limit of 0.301 nM (S/N = 3). The fluorescent aptasensor was also validated by SME-spiked human serum samples, showing average recoveries ranging from 96.40 % to 109.30 %, with a relative standard deviation below 10.45 %. Furthermore, when tested on six human serum samples, the aptasensor results were consistent with those obtained from the commercial ELISA method. These findings demonstrate that the proposed aptasensor provides a promising approach for the practical monitoring of low-abundant SME in human serum.

Development of a CRISPR/Cas12a-facilitated fluorescent aptasensor for sensitive detection of small molecules

The integration of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) and CRISPR-associated proteins (Cas) exhibits superior performance in biosensor construction. And the distinctive role of aptamers in target recognition has long been a focal point of research. Through the combination of Cas12a with cis-cleavage activity and aptamer with specific recognition, a simple and rapid fluorescent biosensor has been constructed. Interestingly, with modified fluorescent and quenching groups at two ends, aptamers play a dual role: primarily as the elements for target recognition and additionally functioning act as the fluorescent probe for signal output. Coupling with cis-cleavage of Cas12a, the demand of additional signal probes is eliminated, thus simplifying the reaction system and enhancing result accuracy. Taking okadaic acid (OA) as a representative small molecule model to evaluate the sensor's performance, a simple and straightforward detection method was established. Following this, the universality of the constructed fluorescent aptasensor was validated by incorporating an adenosine triphosphate (ATP) aptamer. Consequently, the CRISPR/Cas12a-assisted aptasensor was demonstrated to serve as a versatile detection platform for small molecules in food safety and clinical diagnostics. In the forthcoming research endeavors, it can be further extended for applications in environmental analysis and various other fields.

A turn-on fluorescent aptasensor for Pb2+ detection based on rhodamine B dye leakage from the internal cavity of hollow gold nanoparticles

In this project, a sensitive fluorescent aptasensor was fabricated to detect lead ions (Pb2+) by applying hollow gold nanoparticles (HGNPs) as a nano-carrier and rhodamine B (RDB) fluorescent dye as the signal agent. In the aptasensor that was created, the specific attachment of the aptamers to Pb2+ ions led to the release of aptamer from the chitosan (CTS) coated-HGNPs loaded with RDB, causing an increase in fluorescence intensity due to the leakage of RDB. The method demonstrated specific detection of the target analyte, achieving a detection limit (LOD) of 1 ppb and a broad linear dynamic range spanning from 2 to 1000 ppb. The aptasensor was able to accurately measure the concentration of Pb2+ in human serum, low-fat milk, and mineral water samples. The suggested biosensor, which offers the benefits of simplicity, user-friendliness, affordability, and high sensitivity, is well-suited for use with complex samples such as environmental and clinical samples.

A ratiometric fluorescent biosensing platform based on CDs and AuNCs@CGO for patulin detection

BackgroundPatulin (PAT) is a mycotoxin, usually found in fruit and their products, that can potentially be harmful to human health. In order to achieve rapid detection of mycotoxins and ensure the safety of food. This study reported a novel ratiometric fluorescent aptasensor for PAT detection. In this study, we used aptamer as the recognition element, Hybrid double stranded modified with fluorescent substances as the fluorescent donor, and AuNCs@CGO as the fluorescent acceptor. After the addition of PAT, the ratiometric fluorescence “turn on” response was exhibited. ResultsThe AuNCs@CGO are obtained by amide reaction between BSA-AuNCs and carboxylated graphene oxide (CGO). The prepared AuNCs@CGO can shorten the time of FRET effect and exhibit highly efficient quenching ability by adsorption effects (π-π stacking and electrostatic gravity) on the Aptamer-modified CDs. When the target PAT bound specifically to the CDs-apt, the fluorescence of the CDs-apt would recover, while the fluorescence of ROX modified cDNA remained unchanged. This ratiometric fluorescence response improved the accuracy of PAT detection. In addition, the proposed had good linearity for PAT in the range of 0.1–50 ng/mL with a limit of detection 0.16 ng/mL. The recovery of standard addition in grapes were 95.9%–105.4 %. SignificanceAn effective fluorescent detection method for PAT was constructed based on aptamer and nanomaterials. This new fluorescent biosensor has the characteristics of simple synthesis, easy operation, high sensitivity, strong selectivity and a low LOD, which may be a promising idea and platform for the detection of food safety hazard factors.

Fluorescent aptasensor based on competitive recognition strategies and point-of-care testing system for brain natriuretic peptide detection

Brain natriuretic peptide (BNP) is the preferred biomarker for clinical analysis, widely used in early screening and prognostic monitoring of cardiovascular and neurological diseases. Due to the low concentration and short half-life of BNP in the blood, its sensitive detection remains a challenge that must be overcome. With the rapid development of molecular diagnosis and point-of-care testing (POCT), developing a BNP biosensor with high sensitivity, good stability, accuracy, speed, and low-cost is of great significance for clinical applications and emergency diagnosis. However, BNP in human blood exists in various forms, and traditional fluorescence sensors may lead to overestimation of the concentration. In this work, we constructed an “on” fluorescent aptasensor based on competitive recognition strategy for quantitative detection of BNP, and built a fluorescence sensing detection system based on smartphone to achieve rapid on-site detection. We designed a specific aptamer labeled with carboxyfluorescein (FAM) with a simple structure and high biological affinity for selective capture of BNP, and utilized the large specific surface area and excellent fluorescence quenching effect of carboxylated graphene oxide (GO-COOH) as a carrier and quencher for the aptasensor. By optimizing experimental parameters such as aptamer and GO-COOH concentrations, as well as quenching/recovery time, linear sensitive detection of BNP was achieved in the concentration range of 0.01 ng/mL–10 ng/mL, with a detection limit as low as 10 pg/mL, good specificity, and excellent application potential in artificial serum spiking experiments. Additionally, a stable and sensitive fluorescence signal collection system has been developed to meet the needs of portable detection, breaking through the usage environment of traditional fluorescence detection equipment and filling the gap of portable fluorescence biosensing. In summary, we have creatively proposed a fluorescent aptasensor that enables rapid and sensitive detection of BNP and the development of low-cost fluorescent biosensors. The combination with POCT has shown broad application prospects and also provides some ideas for the fluorescence detection of other protein biomarkers.

A dual-mode aptasensor based on rolling circle amplification enriched G-quadruplex for highly sensitive IFN-γ detection

BackgroundAptasensors have been extensively utilized in target detection due to their advantages of high sensitivity and fast response. However, the reliability of the detection results of the single-mode aptasensor cannot be verified in time. Developing efficient detection methods with cross-validation capability is beneficial to achieving highly reliable detection. This study aims to design a colorimetric and fluorescent dual-mode aptasensor by skillfully engineering G-quadruplex assembly and rolling circle amplification for highly reliable IFN-γ detection. ResultsThe complexes of anti–IFN–γ aptamers and complement sequences (cDNA) were modified on the magnetic beads. In the presence of IFN-γ, the preferential combination of aptamers with IFN-γ resulted in the release of cDNAs. The cDNAs were collected by magnetic separation and then used as primers to trigger rolling circle amplification reaction to generate enriched G-quadruplexes. The G-quadruplex could be utilized to combine with hemin to catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine for colormetric mode or to couple with the fluorogenic dye Thioflavin T for fluorescent mode. The developed dual-mode aptasensor displayed a linear range of 1–10000 pM with a detection limit of 0.406 pM for the colormetric mode and a range of 0.1–10000 pM with a detection limit of 0.037 pM for the fluorescent mode. Further, the designed aptasensor was applied to IFN-γ detection in serum samples and achieved satisfactory recoveries. SignificanceThis innovative dual-mode detection strategy skillfully leverages the effective target-binding ability of aptamer, dual-function of the G-quadruplex and the signal amplifying ability of rolling circle amplification. This approach not only provides a reliable testing tool for the detection of IFN-γ, but also promotes the development of multimode sensing platforms.

Perylene Diimide-based Fluorescent Aptasensor for Quantitative Analysis of Pb2+ Based on Terminal Deoxynucleotidyl Transferase-assisted Formation of Elongated Aptamer and Gold Nanoparticles.

Due to the exceedingly poisonous properties of Pb2+, it is imperative to conduct a thorough assessment of its quantity in both biological and environmental samples, as this is crucial for safeguarding public health. This study describes an economic turn-off fluorescent aptasensor for the quantitative analysis of Pb2+ employing 3,4,9,10-perylenetetracarboxylic acid diimide (PTCDI) as a cost-effective fluorophore, gold nanoparticles (AuNPs) as separating agent and an elongated aptamer as both targeting agent and PTCDI loading site. The fundamental principle of the suggested fluorescent aptasensor, which is based on PTCDI, relies on detecting variations in the fluorescence intensity of PTCDI when an elongated aptamer (as single-stranded DNA) is present or absent. The advanced aptasensor is advantageous due to the elongation of the lead aptamer sequence length induced by terminal deoxynucleotidyl transferase (TdT), resulting in enhanced sensitivity. The presence of Pb2+ and the centrifugation process causes the separation of the poly A-modified aptamer/Pb2+ conjugate from the poly T sequence. Hence, the interaction of PTCDI with the poly A moiety in the modified aptamer leads to a decrease in its fluorescence emission. The findings showcased that the fluorescent aptasensor exhibited exceptional specificity towards Pb2+ ions, while the biosensing platform accomplished an impressive detection limit of 3.7pM. Moreover, the suggested aptasensor utilizing PTCDI exhibits a commendable capability in quantitatively analyzing Pb2+ within human serum samples and mineral water.

Thylakoid-based green preparation of porous microneedles for antibiotic residues detection in food samples

BackgroundAntibiotic residues in food chain have raised concerns regarding their toxicity and involvement in antimicrobial resistance. However, most existing antibiotic biosensors are primarily applicable to liquid food samples. Given the complex matrix characteristics of foods, there is an urgent need for the development of effective antibiotic detection platforms that exhibit high universality and flexibility. Porous microneedles (PMN) are microdevice structures with needle-like shapes and microscale pores throughout their composition, which facilitate rapid sampling. Consequently, the integration of PMN with biosensors holds significant promise for the detection of antibiotic residues in complex food samples. ResultsIn this study, hydrogel-forming PMN are fabricated by leveraging the oxygen-production capacity of thylakoid to generate bubbles and form porous structures. These PMN are then integrated with a fluorescence aptasensor for the quantification of the antibiotic netilmicin. The aptasensor consists of a netilmicin (NET) aptamer with stem loop and hairpin structure, which facilitated the binding of SYBR Green I to produce a fluorescent signal. In the presence of NET, the complete binding between NET and the aptamer results in a reduction of fluorescence intensity, thereby generating a detectable signal change for the detection of NET. Utilizing capillary action accelerate fluid extraction (2.9 times faster than nonporous microneedles) and a large specific surface area (5.1072 m2/g) conducive to aptasensor adsorb, the PMN achieve efficient capture and quantification of antibiotic with limits of detection and quantitation of 5.99 nM and 19.8 nM, respectively. SignificancePorous microneedles with tunable porosity and desirable mechanical properties are successfully fabricated. The integration of PMN with aptasensor enable the efficient detection of netilmicin in fish, milk and river water samples, demonstrating high recovery rates. The PMN represent potential tools for the convenient and rapid detection of antibiotic residues within complex food matrices, thereby enhancing food safety monitoring.

Plasmon-enhanced fluorescence and electrochemical aptasensor for SARS-CoV-2 Spike protein detection

In this work, we combined plasmon-enhanced fluorescence and electrochemical (PEF-EC) transduction mechanisms to realize a highly sensitive dual-transducer aptasensor. To implement two traducers in one biosensor, a novel large-scale nanoimprint lithography process was introduced to fabricate gold nanopit arrays (AuNpA) with unique fringe structures. Light transmitting through the AuNpA samples exhibited a surface plasmon polariton peak overlapping with the excitation peak of the C7 aptamer-associated fluorophore methylene blue (MB). We observed a five and seven-times higher average fluorescence intensity over the AuNpA and fringe structure, respectively, in comparison to a plane Au film. Furthermore, the MB fluorophore was simultaneously utilized as a redox probe for electrochemical investigations and is described here as a dual transduction label for the first time. The novel dual transducer system was deployed for the detection of SARS-CoV-2 Spike protein via a C7 aptamer in combination with a strand displacement protocol. The PEF transducer exhibited a detection range from 1 fg/mL to 10 ng/mL with a detection limit of 0.07 fg/mL, while the EC traducer showed an extended dynamic range from 1 fg/mL to 100 ng/mL with a detection limit of 0.15 fg/mL. This work provides insights into an easy-to-perform, large-scale fabrication process for nanostructures enabling plasmon-enhanced fluorescence, and the development of an advanced but universal aptasensor platform.

Ultrastable NAC-Capped CdZnTe Quantum Dots Encapsulated within Dendritic Mesoporous Silica As an Exceptional Tag for Anti-Interference Fluorescence Aptasensor with Signal Amplification.

In this work, we explored the potential of thiol-capped CdZnTe quantum dots (QDs) as an exceptional signal tag for fluorescence aptasensing applications. Employing a one-pot hydrothermal approach, we modulated the terminal functional groups of CdZnTe QDs using l-cysteine (Lcys), 3-mercaptopropionic acid (MPA), and N-acetyl-l-cysteine (NAC) as ligands. Our comparative analysis revealed that NAC-capped CdZnTe QDs (NAC-CdZnTe QDs) exhibited superior anti-interference capabilities and storage stability across various temperatures, pH levels, and storage durations. Encouraged by these promising results, we further optimized the use of ultrastable NAC-CdZnTe QDs encapsulated in dendritic mesoporous silica nanoparticles (DMSN@QDs) as an exceptional tag for the development of an advanced anti-interference fluorescence aptasensor for aflatoxin B1 (AFB1) detection. The developed aptasensor using DMSN@QDs as signal tags achieved a remarkable signal amplification of approximately 10.2 fold compared to the NAC-CdZnTe QDs coated silica (SiO2@QDs) labeled fluorescence aptasensor. This aptasensor was able to detect AFB1 within a wide range of 1 pg mL-1 to 200 ng mL-1, achieving a limit of detection as low as 0.41 pg mL-1 (S/N = 3). Crucially, the specific binding affinity between the aptamer and the target enabled the aptasensor to be easily customized for various targets by simply replacing the aptamer sequence with the desired one. The exceptional potential of NAC-CdZnTe QDs, particularly when encapsulated in DMSNs, leads to the development of highly sensitive and selective anti-interference fluorescence aptasensors for various targets, thereby, paving the way for advancements in a diverse range of applications.

A novel red emission carbon quantum dots-based aptasensor for detection of potassium ions in vitro and in vivo and its application in plant imaging

The determination of potassium ion (K+) concentration in organisms is of particular importance. Herein, an efficient, sensitive, and eco-friendly fluorescence aptasensor for detecting potassium ions (K+) was designed based on the interaction of aptamer (K-Apt), complementary sequence of aptamer (C-Apt), red emission carbon quantum dots (R-CDs), and graphene oxide (GO). Red luminescent CDs modified with K+ aptamer(R-CDs@K-Apt) and C-Apt modified GO (C-Apt@GO) were used as the fluorescence donor and acceptor, respectively, in this aptasensor. K+ was detected sensitively using the fluorescence resonance energy transfer (FRET) method. The linear range of this aptasensor was 5.0 × 10−9–2.2 × 10−7 mol/L, and its detection limit was as low as 6.2 × 10−11 mol/L. Importantly, this aptasensor can be employed for quantitative K+ detection in serum because of the enhancement of its selectivity and biocompatibility by the modification of biomolecules including K-Apt and C-Apt. Furthermore, the aptasensor’s red emission at 625 nm enabled it to completely avoid the background fluorescence caused by chlorophyll in wheat seedlings, allowing it to display the K+ concentration of the wheat through plant imaging. These findings lay a foundation for the development of a novel detection technique for analyzing the distribution of K+ in the body fluids of animals and plants.

Fabrication of Glucose Fluorescent Aptasensor Based on CdTe Quantum Dots.

Diabetes is a chronic metabolic disease characterized by high blood glucose (or blood sugar) levels, which harms the heart, blood vessels, eyes, kidneys, and nerves over time. So, it is crucial to regularly control glucose concentration in biological fluids to check its targets, reduce unpleasant symptoms of high and low blood sugar, and avoid long-term diabetes complications. This study developed a simple, rapid, sensitive, and cost-effective fluorescence system for glucose determination. The fluorescent Aptasensor was fabricated using cadmium telluride quantum dots (CdTe QDs) modified with thioglycolic acid and functionalized with thiol-glucose-aptamer through ligand exchange. The thiol-glucose-aptamer interacted directly with CdTe QDs, increasing fluorescence intensity. However, it decreased when the target molecules of glucose were introduced. The structural and morphological characteristics of the Aptasensor were confirmed by various analytical methods such as UV-visible spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive x-ray spectroscopy (EDX), transmission electron microscopy (TEM), atomic force microscopy (AFM), and dynamic light scattering (DLS). According to the typical Stern-Volmer equation, the relationship between fluorescent quenching and target concentration was linear with a detection limit (LOD) of 0.13 ± 1.95 × 10-11 mol L-1 and a relative standard deviation (RSD) of 1.05%. The Aptasensor demonstrated high specificity towards the target and stability over 28 days. Furthermore, it detected glucose in human serum and urine with a recovery rate of up to 99.74%. The results indicate that the fluorescent Aptasensor could be valuable in developing robust sensing technology for low-concentrated analytes.

Novel aptamer fluorescence assays for malachite green and leucomalachite green detection

Simple fluorescence aptasensors were established for malachite green (MG) and leucomalachite green (LMG) detection using G-quadruplex dyes thioflavin T (ThT) and thiazole orange (TO), respectively. ThT and TO, initially non-fluorescent in aqueous solution, exhibited fluorescence upon binding to target-specific aptamers, resulting in the stabilization of G-quadruplex structures. The specific binding between G-quadruplex and MG could induce conformational changes, which caused a pronounced quenching of fluorescence emitted by the intercalator, providing a possibility for detection. The developed assays demonstrated a good linear relationship in the range of 0–1000 μg L-1 for MG and 0–250 μg L-1 for LMG, with low limits of detection of 5.4 × 10-3 μg L-1 and 0.1 μg L-1 respectively. More importantly, satisfactory detection results in water and fish samples were obtained. Noteworthy was that the uncomplicated fluorescent aptasensors operated effectively without the need for any modifications. The experimental process was facile and realized in homogeneous solution, which exhibited quick responsiveness after simple mixing.