Fluorescence Resonance Energy Transfer Aptasensor Research Articles

Development of a FRET aptasensor based on MoS2-doped Zn-MOF as luminophore for selective detection of cadmium in aqueous solutions.

A robust "on-off" fluorescent aptasensor was developed using nanohybrids of molybdenum sulfide (MoS2) quantum dot (QD)-doped zinc metal-organic frameworks (Zn-MOF) for selective and sensitive detection of cadmium ions (Cd2+) in water. This nanohybrid (MoS2@Zn-MOF), synthesized via "bottle around the ship" methodology, exhibited a high-intensity fluorescence emission centered at 430nm (λEm) (blue) on excitation at 320nm (λEx). Further, the conjugation of this fluorophore to phosphate-modified cadmium aptamer (Cd-2-2) was achieved through carbodiimide reaction. The hybridization of prepared sensing probe (MoS2@Zn-MOF/Cd-2-2 aptamer) was done with dabcyl-conjugated complementary DNA (cDNA), acting as energy donor-acceptor pair in the fluorescence resonance energy transfer (FRET) system. This hybridizationcauses the fluorescence quenching of the nanohybrid. In the presence of Cd2+, the aptamer from the fabricated nano-biosensing probe binds to these ions, resulting in release of dabcyl-cDNA oligomer. This release of dabcyl-cDNA oligomer from the sensing probes restores the fluorescence of the nanohybrid. Under optimized conditions (sensing probe/dabcyl-cDNA ratio 1/7, pH 7.4, and temp 28°C), the sensing probe showed a fast response time of 1min. The fluorescence intensity of the nanohybrid can be utilizedto determine the concentration of Cd2+. The proposed aptasensor achieved highly sensitive detection of Cd2+ with a limit of detection (LOD) of 0.24ppb over the range of 1 × 10-9 to 1 × 10-4M along with minimal effects of interferences (e.g., Hg2+, Pb2+, and Zn2+) and good reproducibility. The designed aptasensor based on MoS2@Zn-MOF nanofluorophore offers a highly sensitive and selective approach for rapid screening of metal ions in aqueous environments.

Highly sensitive and specific graphene oxide-based FRET aptasensor for quantitative detection of human soluble growth stimulating gene protein 2

Soluble growth stimulation expressed gene 2 (sST2) is a new generation biomarker in the diagnosis and prognosis of heart failure (HF). Here, the sST2-specific aptamers were selected from a random ssDNA library with the full length of 88 nucleotides (nt) via target-immobilized magnetic beads (MB)-based systematic evolution of ligands by exponential enrichment (SELEX) technology. After eight rounds of selection, six aptamers with the most enrichment were selected. Among, the aptamer L1 showed the high-affinity binding to sST2 with the lowest Kd value (77.3 ± 0.05 nM), which was chosen as the optimal aptamer for further molecular docking. Then, the aptamer L1 was used to construct a graphene oxide (GO) - based fluorescence resonance energy transfer (FRET) biosensor for sST2, which exhibits a linear detection range of 0.1–100 μg/ml and a detection limit of 3.7 ng/ml. The aptasensor was applied to detect sST2 in real samples, with a good correlation and agreement with the traditional enzyme-linked immunosorbent assay (ELISA) when quantitative analyzing the sST2 concentration in serum samples from HF patients. The results show that not only an efficient strategy for screening the practicable aptamer, but also a rapid and sensitive detection platform for sST2 were established.

A Fluorescence Resonance Energy Transfer Aptasensor for Aflatoxin B1 Based on Ligand-Induced ssDNA Displacement

In this study, a fluorescence resonance energy transfer (FRET)-based aptasensor for the detection of aflatoxin B1 (AFB1) was designed using a carboxyfluorescein (FAM)-labeled aptamer and short complementary DNA (cDNA) labeled with low molecular quencher RTQ1. The sensing principle was based on the detection of restored FAM-aptamer fluorescence due to the ligand-induced displacement of cDNA in the presence of AFB1, leading to the destruction of the aptamer/cDNA duplex and preventing the convergence of FAM and RTQ1 at the effective FRET distance. Under optimal sensing conditions, a linear correlation was obtained between the fluorescence intensity of the FAM-aptamer and the AFB1 concentration in the range of 2.5–208.3 ng/mL with the detection limit of the assay equal to 0.2 ng/mL. The assay time was 30 min. The proposed FRET aptasensor has been successfully validated by analyzing white wine and corn flour samples, with recovery ranging from 76.7% to 91.9% and 84.0% to 86.5%, respectively. This work demonstrates the possibilities of labeled cDNA as an effective and easily accessible tool for sensitive AFB1 detection. The homogeneous FRET aptasensor is an appropriate choice for contaminant screening in complex matrices.

A "turn-on" fluorescence resonance energy transfer aptasensor based on carbon dots and gold nanoparticles for 17β-estradiol detection in sea salt.

17β-estradiol is abused in the food industry. Excess 17β-estradiol can disturb the endocrine system or cause many diseases including obesity, diabetes, cardiac-cerebral vascular disease, and cancers in the human body. A "turn-on" fluorescence resonance energy transfer (FRET) aptasensor based on carbon dots (CDs) and gold nanoparticles (AuNPs) was developed for the detection of 17β-estradiol. A thiol-modified oligonucleotide was conjugated to AuNPs and amino modified oligonucleotide was linked to CDs. The 17β-estradiol aptamer was hybridized with the two oligonucleotides, shortening the distance between CDs and AuNPs. With 360 nm UV light excitation, FRET occurred between CDs and AuNPs. The system was "turn-off". When 17β-estradiol was detected, the aptamer specifically bound to 17β-estradiol, and the FRET system was destroyed, leading to the "turn-on" phenomenon. The fluorescence intensity recovery was detected in the concentration range of 400 pM to 5.5 μM. The limit of detection (LOD) was 245 pM. The FRET aptasensor demonstrated good selectivity for 17β-estradiol detection. Reasonable spiked recoveries were obtained in sea salt samples. It showed the potential for estrogen detection in food safety and environmental applications.

Fluorescence Resonance Energy Transfer Aptasensor of Ochratoxin A Constructed Based on Gold Nanorods and DNA Tetrahedrons.

Ochratoxin A (OTA) contamination of corn has received significant attention due to the wide distribution and high toxicity of OTA. The maximum residue limit standard of OTA in corn has been established by the Chinese Government and other unions. Nanoparticle-based fluorescence resonance energy transfer (FRET) assays are promising methods for the sensitive and fast detection of OTA. However, satisfactory detection sensitivity is commonly achieved with complicated signal amplification processes or specific nanoparticle morphologies, which means that these assays are not conducive to fast detection. This study proposes a simple and novel strategy to improve the sensitivity of FRET aptasensors. In this strategy, a DNA tetrahedron was first used in gold nanorod-based FRET aptasensors. DNA tetrahedron-modified gold nanorods are used as fluorescent acceptors, and Cy5-modified complementary sequences of the OTA aptamer are used as fluorescent donors. The aptamers of OTA are embedded in the DNA tetrahedrons, and FRET occurs when the aptamers hybridize with the Cy5-modified complementary sequences. The aptamer-integrated DNA tetrahedron modified on the surface of gold nanorods acts as an anchor, thus avoiding the crowding and entanglement of aptamers. Due to the competitive combination between the OTA aptamers and complementary sequences, the greater the amount of OTA, the less the amount of Cy5-modified complementary sequences that bind with the aptamers and the less the amount of Cy5 that is quenched. Thus, the fluorescence intensity is positively related to the OTA concentration. In this study, in the concentration range of 0.01-10 ng/mL, the fluorescence intensity was found to be linearly related to the logarithmic concentration of OTA. The limit of detection was calculated to be 0.005 ng/mL. The specificity of the developed biosensor was demonstrated to be efficient. The accuracy and stability of the developed aptasensor were also tested, and the method exhibited good performance in real samples.

Detection of pathogenic bacteria in milk and whey samples using a fluorescence resonance energy transfer aptasensor based on cerium oxide nanoparticles.

Herein, we present a facile and sensitive fluorescence resonance energy transfer (FRET) aptasensor for the detection of pathogenic bacteria, where antibiotic-functionalized cerium oxide nanoparticles were served as an energy donor and aptamer-modified gold nanoparticles (aptamer-AuNPs) were employed as an energy acceptor. To illustrate the feasibility of this strategy, Escherichia coli (E. coli) was examined. The strategy for the detection of E. coli bacteria as a target molecule is described using the FRET pair of azithromycin-functionalized CeO2 nanoparticles (Azm-CeO2NPs) and aptamer-AuNPs. The spectral overlap between these two nanoparticles and Azm and the aptamer binding on the surface of E. coli specifically provides the condition, which leads to the occurrence of the FRET phenomenon. In this way, a good linear correlation between the fluorescence intensity of Azm-CeO2NPs and E. coli concentration was obtained in the range of 10-1.5 × 105 cfu mL-1. The detection limit of the proposed method at a signal to noise ratio of 3 (3σ) was estimated to be 1.04 cfu mL-1. Further, the proposed method was applied to detect E. coli in real samples within 30 min, which indicates the applicability of the proposed method. This method could be used for other pathogenic bacterium recognition or synchronous detection by employing molecules that are particular to the desired bacteria.

Cationic conjugated polymer-based FRET aptasensor for label-free and ultrasensitive ractopamine detection.

A label-free fluorescence resonance energy transfer (FRET) platform based on cationic conjugated polymers and aptamers for ultrasensitive and specific ractopamine detection was constructed. This method exhibited a wide linear range from 0.05 to 500 μM and a low limit of detection of 47 nM, which make it an attractive assay platform for foodborne doping.

The systemic characterization of aptamer cocktail for bacterial detection studied by graphene oxide-based fluorescence resonance energy transfer aptasensor.

Aptamers have gained significant attention as the molecular recognition element to replace antibodies in sensor development and target delivery. Nevertheless, it is noteworthy that unlike the wide application of polyvalent antibodies, existing researches on the combined use of heterologous aptamers with similar recognition affinity and specificity for target detection were sporadic. Herein, first, the wide existence of polyaptamer for bacteria was revealed through the summary of existing literature. Furthermore, based on the establishment of a sensitive aptamer cocktail/graphene oxide fluorescence resonance energy transfer polyaptasensor with a detection limit as low as 10CFU/ml, the systemic characterization of aptamer cocktails in bacterial detection was carried out by taking E. coli, Vi. parahemolyticus, S. typhimurium, and C. sakazakii as the assay targets. It was turned out that the polyaptasensors for C. sakazakii and S. typhimurium owned prevalence in the broader concentration range of target bacteria. While the polyaptasensors for E. coli and V. parahemolyticus outperformed monoaptasensor mainly in the lower concentration of target bacteria. The linear relationships between fluorescence recovery and the concentration of bacteria were also discussed. The different characteristics of the bacterial cellular membrane, including the binding affinity and the robustness to variation, are analyzed to be the main reason for the diverse detection performance of aptasensors. The study here enhances a sensor detection strategy with super sensitivity. More importantly, this systemic study on the aptamer cocktail in reference to antibodies will advance the in-depth understanding and rational design of aptamer based biological recognition, detection, and targeting.

A "turn-on" FRET aptasensor based on the metal-organic framework-derived porous carbon and silver nanoclusters for zearalenone determination

Zearalenone (ZEN) is a fungal secondary metabolite with an estrogen-like structure. Its widespread existence and potential hazards to human and animal health call for alternative rapid determination methods to monitor ZEN in food and the environment. Herein, a robust and enzyme-free "turn-on" aptasensor based on fluorescence resonance energy transfer (FRET) was developed for the sensitive identification of ZEN. Aptamer-modified silver nanoclusters (AgNCs) and porous Fe3O4/carbon octahedra derived from the metal-organic framework (MOF) acted as the FRET energy donor−acceptor pair in fluorescence quenching. DNA-templated AgNCs can be adsorbed onto the surface of porous Fe3O4/carbon octahedra through π-π stacking, which will lead to the FL quenching of AgNCs. However, in the presence of the ZEN, the formation of the ZEN/aptamer complex promoted the release of AgNCs and thereby brought about the recovery of fluorescence, which can be used to indicate the concentration of ZEN. The prepared aptasensor was characterized by various physicochemical techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM), powder X-ray diffraction (PXRD), energy-dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS) and circular dichroism spectroscopy (CD). By combining the excellent quenching properties and easy separation of magnetic porous Fe3O4/carbon octahedra, as well as the appealing photostability and water solubility of AgNCs, the proposed FRET platform demonstrated superior analytical performance with a linear range of 0.01–250 ng mL−1 and a LOD as low as 2 × 10−3 ng mL−1. Most importantly, the practicability and reliability of the FRET-based strategy were confirmed by conducting the determination of ZEN in real samples.

2D titanium carbide nanosheets based fluorescent aptasensor for sensitive detection of thrombin

The emerging two-dimensional titanium carbides (MXenes) have a large potential in biomedical sensing owing to their excellent electrical and optical properties. Herein, a fluorescence resonance energy transfer (FRET) aptasensor with high sensitivity and specificity was constructed with single layer Ti3C2 MXene for quantitative detection of thrombin. The dye labelled thrombin-binding aptamer (TBA) was deposited on the surface of Ti3C2, and the fluorescence of which was efficiently quenched owing to the FRET between the dye and Ti3C2. The fact that thrombin forms quadruplex with TBA on Ti3C2 surface is due to the high electronic affinity between thrombin and Ti3C2. This process will cause the subsequent detachment of dye from the surface of Ti3C2, resulting in the recovery of fluorescence. Because of the special structure and high fluorescence quenching efficiency of Ti3C2 MXene, the aptasensor shows a high sensitivity with a low detection limit for thrombin at 5.27 pM. Three different aptamers were compared, and the aptamer HD22 is most sensitive for detection of thrombin originated from its great specificity in the human plasma. Importantly, this Ti3C2 MXene-based FRET aptasensor can detect thrombin in human serum accurately. These results suggest that the Ti3C2 MXene-based FRET aptasensor hold a great prospect in clinical diagnosis in the real-world applications.

Ratiometric fluorescence resonance energy transfer aptasensor for highly sensitive and selective detection of Acinetobacter baumannii bacteria in urine sample using carbon dots as optical nanoprobes

Development of sensitive and selective analytical method for accurate diagnosis of Acinetobacter baumannii (Ab) bacteria in biological samples is a challenge. Herein, we developed an ingenious ratiometric fluorescent aptasensor for sensitive and selective detection of (Ab) bacteria based on fluorescence resonance energy transfer (FRET) between ortho-phenylenediamines carbon dot (o-CD), nitrogen-doped carbon nanodots (NCND) as donor's species and graphene oxide (GO) as acceptor. NCND that assembled onto the edge of graphene oxide (GO) exhibited quenched photoluminescence emission, and with the absorption of the modified o-CD with aptamer (o-CD-ssDNA) onto the graphene oxide surface the fluorescence of o-CD was efficiently quenched. The aptamer (ssDNA) as a biorecognition element is bound with A. baumannii specifically which releases the o-CD-ssDNA from GO and the recovery of the fluorescence signal of o-CD, while the fluorescence intensity of NCND only slightly altered and acted as the reference signal in ratiometric fluorescence assay. The fluorescence intensity ratio (I550 nm/I440nm) varied from 2.0 to 10.0 with the concentration of bacteria changing from 2.0 × 103 to 4.5 × 107 cfu/mL and the low detection limit of 3.0 × 102 cfu/mL (S/N = 3). The feasibility of the developed aptasensor for selective detection of A. baumannii in urine sample with satisfactory results was also demonstrated.

A “on-off-on” fluorescence aptasensor using carbon quantum dots and graphene oxide for ultrasensitive detection of the major shellfish allergen Arginine kinase

Shellfish allergy is a crucial public health problem and a severe food safety issue, resulting in an urgent need for an accurate, simple and sensitive method to detect the shellfish allergens in complex food systems. Herein, we have desighed an “on-off-on” fluorescence aptasensor based on fluorescence resonance energy transfer (FRET) using prepared carboxyl groups functionalized CQDs (cCQDs) and graphene oxide (GO) for the detection and quantification of the major shellfish allergen arginine kinase (AK). The FRET aptasensor allowed for the sensitive detection of AK in the range of 0.001–10 μg/mL with the limit of detection (LOD) of 0.14 ng/mL (S/N = 3), and the limit of quantitation (LOQ) of 0.27 ng/mL (S/N = 10). This reliable, accurate and specific aptasensor with user-friendly operation may provide new perspectives in the application of fluorescence technologies for food allergens detection in the field of food safety.

DNA-functionalized dye-loaded carbon dots: ultrabright FRET platform for ratiometric detection of Hg(II) in serum samples and cell microenvironment

The dual-emission carbon dots (CDs) are used to fabricate an ultra-sensitive and highly selective fluorescence resonance energy transfer (FRET) aptameric-sensor for the quantitation of Hg(II). The designed strategy worked based on hybridization between T-rich ssDNA(S1) immobilized on CDs and AuNPs modified with complementary aptamer (AuNPs-S2) and Rhodamine B (RB) as an extra internal reference. Under optimized experimental conditions, the intensity ratio of I580/I668 shows a good linear relationship with the Hg(II) concentration in concentration range of 1.0 × 10−18 to 50.0 × 10−5 M with detection limit of 5 × 10−19 M. The proposed FRET aptasensor showed high selectivity for Hg(II) determination even in the presence of other metal ions with higher concentration as high as 1000 times. Furthermore, the RB-CDs probe was demonstrated to be efficient for MDA-MB 231 cell imaging. The bifunctional signaling probe exhibits impressive simplicity, convenience, and low detection time and the proposed sensor can be applied in biomedicine study, food safety, and environmental protection.

G-quadruplex specific dye-based ratiometric FRET aptasensor for robust and ultrafast detection of toxin

G-quadruplex specific dyes are powerful tools for probing nucleic acid structures. Among nucleic acids, aptamers are of great interest, and widely exploited to construct versatile bioassays. Herein, based on G-quadruplex selective dye, thioflavin T (ThT), for probing the intrinsic structure of aptamers, we proposed a ratiometric fluorescence resonance energy transfer (FRET) aptasensor enabling robust and ultrafast detection of toxin. The binding of target ochratoxin A (OTA) would destruct the G-quadruplex structure of aptamer. It would lead to the detachment of ThT dye from aptamer which diminished the FRET effect between ThT and terminal-labeled dye, thus allowing quantification of OTA via FRET signals. The FRET aptasensor would confer an enhancement of 76.9% of signal to background ratio compared to the ThT-based non-FRET aptasensor. Remarkably, the FRET mechanism would eliminate the signal fluctuation resulted from varied probe concentration, thus benefiting the robustness of the assay. The aptasensor could achieve a detection of limit of 0.38 ng/mL for OTA detection. And the detection of OTA could be finished within 30 s. Besides, the assay was successful in analyzing OTA in coffee and oat samples with recoveries rate of 93.93%–107.59%. Therefore, G-quadruplex specific dye-based probing and FRET method would be a compelling design strategy for aptasensor, and may facilitate their practical application in food safety and environmental screening.

A fluorescence turn-on biosensor based on gold nanoclusters and aptamer for alpha fetoprotein detection

Alpha-fetoprotein (AFP), an important tumor marker, is widely used for the diagnosis of patients with germ cell tumors and hepatocellular carcinoma. Herein, a highly sensitive aptasensor for AFP detection was constructed based on fluorescence resonance energy transfer (FRET) between 5-carboxyfluorescein (FAM) and gold nanoclusters (AuNCs). AuNCs can effectively quench the fluorescence of FAM-AFP aptamer via strong coordination interactions. When AFP was introduced into the FAM-AFP aptamer-AuNCs FRET system, the AFP aptamer preferentially combined with AFP accompanied by conformational change, which greatly weakened the coordination interaction between the AFP aptamer and AuNCs. Thus, fluorescence recovery of FAM was observed. In the range of 10.0 -100.0 ng/mL, a linear relationship between the fluorescence recovery rate and the concentration of AFP was obtained with the detection limit of 6.631ng/mL. The highly sensitive FRET aptasensor with simple configuration showed promising prospect in detecting a variety of biomarkes.

Silver nanoclusters based FRET aptasensor for sensitive and selective fluorescent detection of T-2 toxin

T-2 is a trichthecenes mycotoxin responsible for severe food poisoning and toxic influences in humans and animals. Therefore, a rapid and sensitive detection of T-2 is an urgent need to protect the public health mainly caused by the consumption of contaminated agricultural products. Herein, we have prepared one pot synthesis of aptamer functionalized silver nanoclusters (apt-AgNCs) for fluorescent detection of T-2 that relies on novel fluorescence resonance energy transfer (FRET). Apt-AgNCs, act as energy donor, were applied as fluorescent sensing probe whose fluorescence was quenched by MoS2 employed as fluorescent acceptor. Introduction of target in proposed bioassay leads to desorption of Apt-AgNCs from MoS2, and recovery of fluorescence in a toxin concentration dependent-manner. A dynamic quantification range was 0.005–500 ng mL−1 while the LOD was 0.93 pg mL−1. Spiking analysis reveals the efficiency and robustness of the developed assembly, with recovery percentages ranged from 89.46% to 102.08% and 90.41% to 107.75% in maize and wheat samples, respectively. The results were cross-verified using standard commercial T-2 EISA kit. In conclusion, developed bioassay may find good utility in testing for risk assessment of T-2 toxin.

A two dimensional metal–organic framework nanosheets-based fluorescence resonance energy transfer aptasensor with circular strand-replacement DNA polymerization target-triggered amplification strategy for homogenous detection of antibiotics

In the study, a novel two dimensional metal–organic framework (Cu-TCPP nanosheets) based fluorescence resonance energy transfer (FRET) aptasensing platform was developed for detecting antibiotics. Cu-TCPP nanosheets were employed for quenching the background fluorescence and circular strand-replacement DNA polymerization (CSRP) for signal amplification. To fulfill the purpose, we designed an aptamer hairpin probe (HP) whose stem can be opened while specifically binding to target. Then the opened HP would bind with the primer. Under the action of polymerase, extension reaction was induced to generate double-stranded DNA (dsDNA), and then the target was released for the next cycle. Finally, SYBR Green I (SG) can bind with dsDNA to produce strong fluorescence response for quantification of target. It's worth mentioning that the fluorescence of HP/SG complex and free SG could be completely quenched by Cu-TCPP nanosheets while that of dsDNA/SG complex wouldn't be affected. Thus, the sensor produced negligible background signals. It can produce 7.5-fold improved S/N compared to a graphene oxide (GO)-based FRET aptasensor. Chloramphenicol (CAP) was chosen as the model analyte to demonstrate the feasibility of the sensor system. The detection range is broad from 0.001 to 10 ng mL−1 with a detection limit down to 0.3 pg mL−1. The proposed assay was label free and can be used in homogenous detection which greatly simplifies the complexity of operations. The strategy opens a new way to develop sensitive, in-situ and simple assay for antibiotics in foods.

Paper-based MoS2 nanosheet-mediated FRET aptasensor for rapid malaria diagnosis

There has been growing interest in the development of paper-based biosensors because their simplicity and low cost are attractive for point-of-care diagnosis, especially in low-resource areas. However, only a limited range of paper materials – primarily chromatography papers – have been incorporated into diagnostics thus far. Here, we investigate the performance of different types of paper in order to develop an aptamer- and MoS2 nanosheet-based sensor relying on fluorescence resonance energy transfer (FRET) to signal the presence of a target protein. An aptamer which binds to a malarial biomarker, Plasmodium lactate dehydrogenase (pLDH), is chosen for this study, as point-of-care diagnostics would be especially advantageous in low-resource areas, such as those where malaria is prevalent. We observe that of all papers tested, a measurable and specific fluorescence recovery can only be produced on the sensor created with printer paper, while no significant fluorescence recovery is generated on sensors made from other types of paper, including chromatography, lens, and filter papers. Therefore, our findings demonstrate the importance of careful material selection for the development of a paper-based diagnostic test, and suggest that commercially-available products such as printer paper may serve as viable materials to develop cost-effective and simple diagnostics.

Palladium Nanoparticles-Based Fluorescence Resonance Energy Transfer Aptasensor for Highly Sensitive Detection of Aflatoxin M₁ in Milk.

A highly sensitive aptasensor for aflatoxin M1 (AFM1) detection was constructed based on fluorescence resonance energy transfer (FRET) between 5-carboxyfluorescein (FAM) and palladium nanoparticles (PdNPs). PdNPs (33 nm) were synthesized through a seed-mediated growth method and exhibited broad and strong absorption in the whole ultraviolet-visible (UV-Vis) range. The strong coordination interaction between nitrogen functional groups of the AFM1 aptamer and PdNPs brought FAM and PdNPs in close proximity, which resulted in the fluorescence quenching of FAM to a maximum extent of 95%. The non-specific fluorescence quenching caused by PdNPs towards fluorescein was negligible. After the introduction of AFM1 into the FAM-AFM1 aptamer-PdNPs FRET system, the AFM1 aptamer preferentially combined with AFM1 accompanied by conformational change, which greatly weakened the coordination interaction between the AFM1 aptamer and PdNPs. Thus, fluorescence recovery of FAM was observed and a linear relationship between the fluorescence recovery and the concentration of AFM1 was obtained in the range of 5–150 pg/mL in aqueous buffer with the detection limit of 1.5 pg/mL. AFM1 detection was also realized in milk samples with a linear detection range from 6 pg/mL to 150 pg/mL. The highly sensitive FRET aptasensor with simple configuration shows promising prospect in detecting a variety of food contaminants.

Fluorescence resonance energy transfer aptasensor between nanoceria and graphene quantum dots for the determination of ochratoxin A

In the present work, colloidal cerium oxide nanoparticles (nanoceria) and graphene quantum dots (GQDs) were firstly synthesized by sol-gel method and pyrolysis respectively, which all have a uniform nano-size and significant fluorescence emission. Due to the fluorescence emission spectrum of nanoceria overlapped the absorption spectrum of GQDs, fluorescence resonance energy transfer (FRET) between nanoceria and GQDs could occur effectively by the electrostatic interaction. Based on it, a sensitive ratiometric fluorescence aptasensor for the determination of ochratoxin A (OTA), a small molecular mycotoxin produced by Aspergillus and Penicillium strains, has been successfully constructed. In which, probe DNA1@nanoceria and DNA2@GQD were designed to complementary with OTA aptamer, both could adsorb each other, leading to the occur of FRET. After adding of OTA aptamer and then introducing of OTA, the FRET would be interrupted/recovered due to the specific affinity of OTA and its aptamer, the fluorescence recovery value would increase with the addition of OTA. Under the optimal experimental conditions (pH 7, mGQD/nanoceria 2, captamer 100 nM, incubation time 30 min), the constructed ratiometric fluorescence aptasensor exhibited a satisfying linear range (0.01–20 ng mL−1), low limit of detection (2.5 pg mL−1) and good selectivity towards OTA, and has been successfully applied for the analysis of real sample peanuts with good accuracy of the recoveries ranged from 90 to 110%.