Smartphone-based kanamycin sensing with ratiometric FRET

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.

Applications of Smartphone-Based Aptasensor for Diverse Targets Detection

Aptamers are a particular class of functional recognition ligands with high specificity and affinity to their targets. As the candidate recognition layer of biosensors, aptamers can be used to sense biomolecules. Aptasensors, aptamer-based biosensors, have been demonstrated to be specific, sensitive, and cost-effective. Furthermore, smartphone-based devices have shown their advantages in binding to aptasensors for point-of-care testing (POCT), which offers an immediate or spontaneous responding time for biological testing. This review describes smartphone-based aptasensors to detect various targets such as metal ions, nucleic acids, proteins, and cells. Additionally, the focus is also on aptasensors-related technologies and configurations.

The quantum dot vs. organic dye conundrum for ratiometric FRET-based biosensors: which one would you chose?

Förster resonance energy transfer (FRET) is a widely used and ideal transduction modality for fluorescent based biosensors as it offers high signal to noise with a visibly detectable signal. While intense efforts are ongoing to improve the limit of detection and dynamic range of biosensors based on biomolecule optimization, the selection of and relative location of the dye remains understudied. Herein, we describe a combined experimental and computational study to systematically compare the nature of the dye, i.e., organic fluorophore (Cy5 or Texas Red) vs. inorganic nanoparticle (QD), and the position of the FRET donor or acceptor on the biomolecular components. Using a recently discovered transcription factor (TF)-deoxyribonucleic acid (DNA) biosensor for progesterone, we examine four different biosensor configurations and report the quantum yield, lifetime, FRET efficiency, IC50, and limit of detection. Fitting the computational models to the empirical data identifies key molecular parameters driving sensor performance in each biosensor configuration. Finally, we provide a set of design parameters to enable one to select the fluorophore system for future intermolecular biosensors using FRET-based conformational regulation in in vitro assays and new diagnostic devices.

Smartphone-based optical spectroscopic platforms for biomedical applications: a review [Invited]

Rapid advancements in smartphone technology have enabled the integration of many optical detection techniques that leverage the embedded functional components and software platform of these sophisticated devices. Over the past few years, several research groups have developed high-resolution smartphone-based optical spectroscopic platforms and demonstrated their usability in different biomedical applications. Such platforms provide unprecedented opportunity to develop point-of-care diagnostics systems, especially for resource-constrained environments. In this review, we discuss the development of smartphone systems for optical spectroscopy and highlight current challenges and potential solutions to improve the scope for their future adaptability.

Resonance Energy Transfer-Based Biosensors for Point-of-Need Diagnosis-Progress and Perspectives

The demand for point-of-need (PON) diagnostics for clinical and other applications is continuing to grow. Much of this demand is currently serviced by biosensors, which combine a bioanalytical sensing element with a transducing device that reports results to the user. Ideally, such devices are easy to use and do not require special skills of the end user. Application-dependent, PON devices may need to be capable of measuring low levels of analytes very rapidly, and it is often helpful if they are also portable. To date, only two transduction modalities, colorimetric lateral flow immunoassays (LFIs) and electrochemical assays, fully meet these requirements and have been widely adopted at the point-of-need. These modalities are either non-quantitative (LFIs) or highly analyte-specific (electrochemical glucose meters), therefore requiring considerable modification if they are to be co-opted for measuring other biomarkers. Förster Resonance Energy Transfer (RET)-based biosensors incorporate a quantitative and highly versatile transduction modality that has been extensively used in biomedical research laboratories. RET-biosensors have not yet been applied at the point-of-need despite its advantages over other established techniques. In this review, we explore and discuss recent developments in the translation of RET-biosensors for PON diagnoses, including their potential benefits and drawbacks.

Target-initiated autonomous synthesis of metal-ion dependent DNAzymes for label-free and amplified fluorescence detection of kanamycin in milk samples

Accurate and sensitive monitoring of the abused antibiotics is vital because excessive antibiotics in human body can cause toxicity to kidney or lead to potential loss of hearing. In this work, we described a label-free and highly sensitive fluorescent aptasensing platform for detecting kanamycin in milk samples based on the synchronization signal amplification of primer exchange reaction (PER) and metal-ion dependent DNAzyme. The target kanamycin binds the aptamer sequence hybridized on a hairpin template and initiates PER for autonomous synthesis of Mg²⁺-dependent DNAzyme sequences with aid of Bst-DNA polymerase at isothermal conditions. Such a synthesis process can be repeated many times to produce lots of DNAzymes to cyclically cleave the rA site in the signal hairpin substrates under the assistance of Mg²⁺ cofactor to liberate numerous free G-quadruplex fragments. The organic dye thioflavin T (ThT) further associates with these G-quadruplex fragments to yield substantially intensified fluorescence for sensitive detection of kanamycin with a low detection limit of 0.36 nM. In addition, the developed aptamer sensing method also shows a good selectivity for kanamycin against other interfering antibiotics, and can realize the monitoring of kanamycin added in milk samples, highlighting its potential for sensitive monitoring of trace amount of kanamycin for food safety applications.

Recent Advances in Optical Detection of Aminoglycosides

Aminoglycosides (AGs) are broad-spectrum antibiotics used in both human infection and animal medicine. The overuse of AGs causes undesirable residues in food, leading to serious health problems due to food chain accumulation. In recent years, various methods have been developed to determine AGs in food. Among these methods, fluorescent (FL), colorimetric and chemiluminescent (CL) optical methods possess advantages such as their simple instrumentation, low cost, simple operation, feasibility of realizing visualization, and smartphone imaging. This mini-review summarizes optical assays for the detection of AGs in food developed in recent years. The detection principles for different categories are discussed. Then, the amplification techniques for the ultrasensitive detection of AGs are introduced. We also discuss multiplex methods for the simultaneous detection of AGs. Finally, the challenges and future prospects are discussed in the Conclusions and Perspectives section.