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This study describes an upconversion fluorescent aptasensor based on black phosphorus nanohybrids and self-assembled DNA tetrahedrons dual-amplification strategy for rapid detection of the environmental estrogens bisphenol A (BPA) and 17β-estradiol (E2). Tetrahedron complementary DNAs (T-cDNAs) were self-assembled in an oriented fashion on a 2D nanohybrid composed of black phosphorus (BP) and gold to give a materials of architecture BP-Au@T-cDNAs. In parallel, core-shell upconversion nanoparticles were modified with aptamers (UCNPs@apts) and used as capture probes. On complementary pairing, the BP-Au@T-cDNA quench the fluorescence of UCNPs@apts (measured at an excitation wavelength 808 nm and at main emission peaks at 545 nm and 805 nm.) Compared with single-stranded probes based on black phosphorus and gold, the dual-amplification strategy increases quenching efficiency by nearly 25%-30% and reduces capture time to 10 min. This is due to the higher optical absorption of 2D nanohybrid and the reduction of steric hindrance by T-cDNAs. Exposure to BPA or E2 cause the release of UCNPs@apts from the BP-Au@T-cDNAs due to stronger binding between aptamer and analyte. Hence, fluorescence recovers at 545 nm for BPA and 805 nm for E2. Based on these findings, a dually amplified aptamer assay was constructed that covers the 0.01 to 100 ng mL -1 BPA concentration range, and the 0.1 to 100 ng mL -1 E2 concentration range. The detection limits are 7.8 pg mL -1 and 92 pg mL -1 , respectively. This method was applied to the simultaneous determination of BPA and E2 in spiked samples of water, food, serum and urine. Graphical abstract Schematic presentation of novel quenching probes designed by tetrahedron complementary DNAs oriented self-assembled on the surface of black phosphorus/gold nanohybrids. Combined with aptamer-modified upconversion nanoparticles, a dual-amplification self-assembled fluorescence nanoprobe was constructed for simultaneous detection of BPA and E2.

Bisphenol A (BPA) is one of the endocrine-disrupting chemicals which might cause reproductive and endocrine system diseases, and poses a serious threat to the ecosystem and human health. This paper reports an ultrasensitive sensor for trace BPA detection employing fluorescence resonance energy transfer (FRET) between modified upconversion nanoparticles (UCNPs) and tetramethylrhodamine. To circumvent the problems of low luminous efficiency of FRET and low sensitivity of sensor, the upconversion nanoparticles with very strong fluorescence efficiency were prepared and quantitatively modified. Results showed that the concentrations of amino groups and streptavidin were 43 nmol/mg and 6.12 μg/mg on the surface of the UCNPs, respectively. Under the optimal detection conditions, the peak intensity of UCNPs at 547 nm was linear with the logarithm of the BPA concentration with the detection limit of 0.05 ng/mL. Without complicated pre-processing, the recoveries were in general between 91.0 and 115.0% in tap water, river water, and disposable paper cup water. Therefore, the proposed sensor is suitable for effective sensing of trace BPA in water samples.ᅟ [ABSTRACT FROM AUTHOR]

The ultrasensitive and rapid detection of ricin B toxin (RTB) is essential for food safety and environmental monitoring. Herein, a dual-mode magnetic relaxation switch (MRS) and fluorescence (FL) biosensing strategy was developed to efficiently detect RTB using fluorescent magnetic nanoparticles (MNP 300 @SiO 2 (FITC)). Meanwhile, the as-prepared composite MNP 300 @SiO 2 (FITC) exhibited superior biocompatibility and increased FL readout and was coupled with aptamer (Apt) to form a captured probe. Magnetic nanoparticles, 30 nm in diameter (MNP 30), were coupled to a Blocker to form a paired probe to compete with RTB for Apt binding. The presence of the RTB triggered the dual-mode detection switch, thus, weakening the magnetic and fluorescent signals. Compared with the single-mode detection method, the Δ T 2 and Δ FL intensity here exhibited an excellent linear relationship with logarithm of RTB concentrations at 0.001–500 ng/mL and 0.005–500 ng/mL, and obtained ultrahigh sensitivities of 0.8 pg/mL and 3 pg/mL, respectively. In addition, the dual-mode biosensor gained satisfactory spiked recoveries and relative standard deviations for quantitative detection of spiked RTB in edible oil and tap water samples. To our knowledge, this is the first study to describe the accurate quantification of RTB using a sensitive MRS-FL biosensor. We anticipate that this strategy will provide novel avenues for the development of dual-mode sensing assays. [Display omitted] • Fluorescent magnetic nanoparticles (MNP 300 @SiO 2 (FITC) was synthesized. • A magnetic relaxation fluorescence (MRS-FL) dual-mode biosensor was developed. • MRS mode can quantify RTB with low detection limit (0.8 pg/mL). • FL mode can detect RTB from complex environment. • The proposed approach gained satisfactory spiked recoveries for real samples. [ABSTRACT FROM AUTHOR]

Ultra-sensitive, accurate, and specific diagnostic probes are urgently developed to overcome the limitations of conventional norovirus (NV) probes. Herein, we presented the fabrication of a dual-signal probe using multifunctionalized gold and magnetic nanoparticles hybrid composite (Fe 3 O 4 @Au NPs) carriers for the specific detection of NV by magnetic relaxation-fluorescence bimodal sensing. The dual-specific probes were created by modifying Fe 3 O 4 @Au NPs with antibody (Ab) and aptamer-FAM. The antigen-Ab immunoreaction caused aggregation of Fe 3 O 4 @Au NPs, altering the magnetic relaxation signal; simultaneously, the aptamer-FAM that were originally adsorbed on the Au surface were desorbed and cleaved into the solution in the presence of NV, causing a change in the fluorescence signal. Ultrahigh detection sensitives of 0.38 and 3.45 pg/mL were obtained for the dual-modality detection platform, respectively. Furthermore, two quantitative methods obtained satisfactory spiked recoveries for NV-spiked oyster, scallop, strawberry, and tomato samples, consistent with the results of commercial ELISA kits. The results indicated that this dual-specificity assay not only was ultrasensitive but also markedly boosted analysis reliability and precision. Hence, the dual-mode biosensor exhibits high potential for NV detection in the field of food safety. [Display omitted] • Synthesis of nanoparticle hybrid composite (Fe 3 O 4 @Au NPs) carriers. • Fabrication of ultrahigh sensitivity dual-mode norovirus (NV)-specific probes. • Good recoveries from NV-spiked oyster, scallop, strawberry, and tomato samples. • High potential for NV detection in food safety. [ABSTRACT FROM AUTHOR]

Deoxyribonucleic acid (DNA) is a carrier of genetic information. DNA hybridization is characterized by predictability, diversity, and specificity owing to the strict complementary base-pairing assembly mode, which stimulates the use of DNA to build a variety of nanomachines, including DNA tweezers, motors, walkers, and robots. DNA nanomachines have become prevalent for signal amplification and transformation in the field of biosensing, providing a new method for constructing highly sensitive sensing analysis strategies. DNA tweezers have exhibited unique advantages in biosensing applications owing to their simple structures and fast responses. The two-state conformation of DNA tweezers, the open and closed states, enable them to open and close autonomously after stimulation, thus facilitating the quick detection of corresponding signal changes of different targets. This review discusses the recent progress in the application of DNA nanotweezers in the field of biosensing, and the trends in their development for application in the field of biosensing are summarized. [ABSTRACT FROM AUTHOR]

Nano-biosensors are of great significance for the analysis and detection of important biological targets. Surprisingly, the CRISPR-Cas12a system not only provides us with excellent gene editing capabilities, it also plays an important role in biosensing due to its high base resolution and high levels of sensitivity. However, most CRISPR-Cas12a-based sensors are limited by their recognition and output modes, are therefore only utilized for the detection of nucleic acids using fluorescence as an output signal. In the present study, we further explored the potential application of CRISPR-Cas12a and developed a CRISPR-Cas12a-based fluorescence/colorimetric biosensor (UCNPs-Cas12a/hydrogel-MOF-Cas12a) that provides an efficient targeting system for small molecules and protein targets. These two sensors yield multiple types of signal outputs by converting the target molecule into a deoxyribonucleic acid (DNA) signal input system using aptamers, amplifying the DNA signal by catalyzed hairpin assembly (CHA), and then combining CRISPR-Cas12a with various nanomaterials. UCNPs-Cas12a/hydrogel-MOF-Cas12a exhibited prominent sensitivity and stability for the detection of estradiol (E2) and prostate-specific antigen (PSA), and was successfully applied for the detection of these targets in milk and serum samples. A major advantage of the hydrogel-MOF-Cas12a system is that the signal output can be observed directly. When combined with aptamers and nanomaterials, CRISPR-Cas12a can be used to target multiple targets, with a diverse array of signal outputs. Our findings create a foundation for the development of CRISPR-Cas12a-based technologies for application in the fields of food safety, environmental monitoring, and clinical diagnosis. [Display omitted] • CRISPR-Cas12a and nanomaterials were combined for ultrasensitive detection. • CHA, CRISPR-Cas12a and 2D-MOF achieved triple sensitization. • Aptamers, CHA and crRNA can be designed to detect different targets. • UCNPs-Cas12a and hydrogel-MOF-Cas12a provide intuitive and reliable results. [ABSTRACT FROM AUTHOR]

The development of ultrasensitive, reliable, and facile detection technologies for trace tetrodotoxin (TTX) is challenging. We presented a facile dual-mode aptamer-based biosensor (aptasensor) for ultrasensitive fluorescence and surface-enhanced Raman spectroscopy (SERS) detection of TTX by using gold nanoparticles (AuNPs)-embedded metal-organic framework (MOF) nanohybrids (AuNPs@MIL-101) because of their superior properties. A TTX-specific aptamer labelled with fluorescence and Raman reporter cyanine-3 (Cy3-aptamer) was selected as the recognition element and signal probe. Without immobilisation processing steps, Cy3-aptamers were effectively adsorbed onto the surface of AuNPs@MIL-101, thereby generating both fluorescence quenching and SERS enhancement. The preferential binding of TTX towards the Cy3-aptamer triggered the release of rigid Cy3-aptamer–TTX complexes from the AuNPs@MIL-101 surface, which resulted in recovered fluorescence signals and weakened SERS signals. Switched fluorescence and SERS intensities exhibited excellent linear relationships with logarithms of TTX concentrations of 0.01–300 ng/mL, and ultrahigh detection sensitivities of 6 and 8 pg/mL, respectively, were obtained. Furthermore, two quantitative detection approaches for TTX-spiked puffer fish and clam samples obtained satisfactory spiked recoveries and coefficient of variation (CV) values. Notably, the dual-mode aptasensor also successfully determined natural TTX-contaminated samples, showing excellent practical applications. The results indicated that this dual-mode measurement not only was ultrasensitive and simple but also markedly boosted analysis reliability and precision. This study is the first to propose a dual-mechanism AuNPs@MIL-101-based aptasensor for detection of trace TTX and provides a favourable pathway for developing multimode sensing platforms for various applications. [Display omitted] • A facile fluorescence-SERS aptasensor was developed for ultrasensitive TTX detection using AuNPs@MIL-101 nanohybrids. • The strategy was immobilisation-free and easy to operate based on the adsorption action of AuNPs@MIL-101 and Cy3-aptamer. • AuNPs@MIL-101 towards Cy3-aptamer exhibited the superior properties for fluorescence quenching and SERS enhancement. • Dual-mode detection not only was ultrasensitive and simple but also boosted analysis reliability and precision in foods. [ABSTRACT FROM AUTHOR]

T-2 toxin is a class A trichothecene mycotoxin produced by Fusarium , which exhibits genotoxic, cytotoxic, and immunotoxic effects in animals and humans. In this study, we developed an aptasensor for the sensitive detection of T-2 toxin, which was based on fluorescence resonance energy transfer (FRET), and acted by adjusting the electric potential on the surface of upconversion nanoparticles (UCNPs) and MIL-101(Cr). In addition, it combined the excellent spectral properties of UCNPs with the good adsorption quenching abilities of metal organic frameworks (MOFs). Under the action of π-π stacking interactions, the UCNPs-aptamer was adsorbed onto the surface of MIL-101, leading to fluorescence quenching due to the occurrence of FRET. After the addition of T-2 toxin, owing to its selective binding to the UCNPs-aptamer, the UCNPs-aptamer moved away from MIL-101(Cr), resulting in fluorescence recovery. Moreover, the extent of fluorescence recovery was positively correlated with the concentration of T-2 toxin. The limit of detection (LOD) of this sensor was 0.087 ng mL−1 (S/N = 3), and a good linear correlation was observed between the fluorescence intensity and the T-2 toxin concentration in the range of 0.1–100 ng mL−1. Moreover, the recovery of this method was 97.52–109.53% for corn meal samples (relative standard deviation, RSD = 1.7–2.4%) and 90.81–100.02% for beer samples (RSD = 2.4–2.7%). By adjusting the surface electric potentials, the efficient fluorescence aptasensor combined the advantages of UCNPs and MIL-101(Cr) and allowed the first application of such a system in toxin detection, thereby indicating its potential food sample analysis and biochemical sensing. [Display omitted] • An upconversion fluorescent aptasensor was constructed by adjusting the electric potentials. • The functional modification of UCNPs also regulated the surface potential. • The aptasensor combined the advantages of UCNPs and MIL-101 and was applicable to the real sample. [ABSTRACT FROM AUTHOR]