A time-resolved luminescence aptasensor of ofloxacin based on rolling circle amplification and magnetic separation

A robust tag-free aptasensor for fluorescent detection of kanamycin assisted by signal intensification potency of rolling circle amplification

Rolling circle amplification (RCA) process as an excellent DNA amplifier strategy possesses the merits of high performance and easy operation. In this research, a sensitive RCA-based fluorescent aptasensor was fabricated for the detection of kanamycin residues in food. The aptasensing approach consisted of two main steps; immobilization of biotinylated kanamycin aptamer on streptavidin magnetic beads (SMB) and separation of free complementary strands (CS) from the SMB-aptamer/kanamycin at the first step. For the second step, RCA procedure was applied as signal magnifier and SYBR Green was added as fluorescent indicator dye. The linear relation between the aptasensor response and kanamycin concentration was obtained from 5 nM to 100 nM with the detection limit of 1.93 nM (S/N = 3). The aptasensor displayed satisfactory selectivity among other antibiotics. The developed aptasensor is reliable for monitoring kanamycin in milk as a common foodstuff.

A Dual-Mode Method Based on Aptamer Recognition and Time-Resolved Fluorescence Resonance Energy Transfer for Histamine Detection in Fish

Histamine produced via the secretion of histidine decarboxylase by the bacteria in fish muscles is a toxic biogenic amine and of significant concern in food hygiene, since a high intake can cause poisoning in humans. This study proposed a fluorometric and colorimetric dual-mode specific method for the detection of histamine in fish, based on the fluorescence labeling of a histamine specific aptamer via the quenching and optical properties of gold nanoparticles (AuNPs). Due to the fluorescence resonance energy transfer phenomenon caused by the proximity of AuNPs and NaYF4:Ce/Tb, resulting in the quenching of the fluorescence signal in the detection system, the presence of histamine will compete with AuNPs to capture the aptamer and release it from the AuNP surface, inducing fluorescence recovery. Meanwhile, the combined detection of the two modes showed good linearity with histamine concentration, the linear detection range of the dual-mode synthesis was 0.2-1.0 μmol/L, with a detection limit of 4.57 nmol/L. Thus, this method has good selectivity and was successfully applied to the detection of histamine in fish foodstuffs with the recoveries of 83.39~102.027% and 82.19~105.94% for Trichiurus haumela and Thamnaconus septentrionalis, respectively. In addition, this method was shown to be simple, rapid, and easy to conduct. Through the mutual verification and combined use of the two modes, a highly sensitive, rapid, and accurate dual-mode detection method for the analysis of histamine content in food was established, thereby providing a reference for the monitoring of food freshness.

Rolling Circle Amplification as a Universal Method for the Analysis of a Wide Range of Biological Targets

Detection and quantification of biotargets are important analytical tasks, which are solved using a wide range of various methods. In recent years, methods based on the isothermal amplification of nucleic acids (NAs) have been extensively developed. Among them, a special place is occupied by rolling circle amplification (RCA), which is used not only for the detection of a specific NA but also for the analysis of other biomolecules, and is also a versatile platform for the development of highly sensitive methods and convenient diagnostic devices. The present review reveals a number of methodical aspects of RCA-mediated analysis; in particular, the data on its key molecular participants are presented, the methods for increasing the efficiency and productivity of RCA are described, and different variants of reporter systems are briefly characterized. Differences in the techniques of RCA-mediated analysis of biotargets of various types are shown. Some examples of using different RCA variants for the solution of specific diagnostic problems are given.

A sensitive aptasensor based on rolling circle amplification and G-rich ssDNA/terbium (III) luminescence enhancement for ofloxacin detection in food

As the light-harvesting "antenna", G-rich oligonucleotides (such as the G-quadruplex) can interact with lanthanide (III) to bring a luminescent enhancement response. In this study, phenomenon of luminescent enhancement of G-triplex/terbium (III) (G3/Tb³⁺) and interaction between G3 and Tb³⁺ were first reported and characterized. Based on G3/Tb³⁺ luminescence, a label-free aptasensor for the detection of ofloxacin (OFL) residues in the food was developed. The OFL triggered the action of rolling circle amplification (RCA) allowed for the amplification product of G3-forming sequences in the single-stranded DNA, which promoted the conformational transition of the G3/Tb³⁺ complexes once the addition of Tb³⁺. Under the optimal conditions, the logarithmic correlation between the G3/Tb³⁺ luminescence intensity and the concentration of OFL was found to be linear in the range of 5-1000 pmol L^-1 (R² = 0.9949). The limit of detection was 0.18 pmol L^-1 (3σ/slope). Additionally, the good recoveries of 90.19-108.89 % and the relative standard deviations values of 0.59-5.87 % were obtained in the application of the aptasensor detecting OFL in the practical samples. These results confirmed that the present aptasensor has a good analytical performance and bright prospect for detecting ofloxacin residues in food.

Investigation of a Truncated Aptamer for Ofloxacin Detection Using a Rapid FRET-Based Apta-Assay

In this work, we describe the use of a new truncated aptamer for the determination of ofloxacin (OFL), being a principal quinolone commonly used in both human and animal healthcare. Since the affinity of a 72-mer ssDNA sequence has been previously described without further investigations, this paper demonstrates the first computational prediction of the binding motif between this aptamer and OFL through in silico molecular docking studies. Besides, we suggest the application of the characterized recognition mechanism in a simple FRET (Förster Resonance Energy Transfer) pattern for the rapid aptasensing of the quinolone of interest. Accordingly, our approach harnesses the fluorescence quenching of the fluorescein-tagged aptamer (FAM-APT) induced by its partial hybridization to a tetramethyl rhodamine-labelled complementary ssDNA (TAMRA-cDNA). In such a structure, dye labels brought into close proximity act as a FRET pair. Upon ofloxacin addition, an affinity competition occurs to form a more stable FAM-APT/OFL complex, thus unquenching the FAM-APT signal. Interestingly, the recovered fluorescence intensity was found to correlate well with the antibiotic's concentrations in the range of 0.2-200 μM in HEPES buffer, with a linear response that ranged between 0.2 and 20 μM. The rapid apta-assay achieved limits of detection and quantification of 0.12 and 0.40 μM, respectively. The truncated aptamer has also shown an improved specificity toward OFL than other quinolones, compared to the original full-length aptamer described in previous works. Finally, the practical application of the developed apta-assay was successfully confirmed to detect OFL quinolone in spiked milk samples, with satisfactory recoveries ranging between 97.4% and 111.4%.