Attomolar analyte sensing techniques (AttoSens): a review on a decade of progress on chemical and biosensing nanoplatforms.

Detecting the ultra-low abundance of analytes in real-life samples, such as biological fluids, water, soil, and food, requires the design and development of high-performance biosensing modalities. The breakthrough efforts from the scientific community have led to the realization of sensing technologies that measure the analyte's ultra-trace level, with relevant sensitivity, selectivity, response time, and sampling efficiency, referred to as Attomolar Analyte Sensing Techniques (AttoSens) in this review. In an AttoSens platform, 1 aM detection corresponds to the quantification of 60 target analyte molecules in 100 µL of sample volume. Herein, we review the approaches listed for various sensor probe design, and their sensing strategies that paved the way for the detection of attomolar (aM: 10-18 M) concentration of analytes. A summary of the technological advances made by the diverse AttoSens trends from the past decade is presented.

Metal-Organic Framework-Based Fiber Optic Sensor for Chromium(VI) Detection.

This study demonstrates a novel fiber optic sensing strategy for selective adsorption and rapid detection of Cr(VI) ions by exploiting a suitable metal-organic framework matrix and the characteristic spectral absorption of Cr(VI) at 395 nm wavelength, respectively. U-bent fiber optic sensor (U-FOS) probes that exhibit remarkably high evanescent wave-based absorbance sensitivity were employed to efficiently detect the Cr(VI) ions that are adsorbed to a stable zeolitic imidazolate framework (ZIF-67) matrix immobilized on the probe surface. A facile technique was developed for the fabrication of ZIF-67-coated U-FOS probes (FOS/ZIF-67) involving an in situ deposition process followed by heat treatment. Selectivity of the FOS/ZIF-67 probes to Cr(VI) was confirmed by optical absorption spectral investigations with 14 other heavy metals and interfering ions. The sensor performance was evaluated with a compact light-emitting diode-photodetector-based setup. FOS/ZIF-67 probes demonstrate an ability to detect Cr(VI) ions with a limit of detection of 1 ppb and a wide linear dynamic range from 0.005 to 100 ppm within a short response time of 5 to 10 min. These sensors show good recovery rates with real water samples and a shelf-life of at least 4 weeks under ambient conditions, thereby demonstrating their viability for real-world application.

Plasmonic biosensors for bacterial endotoxin detection on biomimetic C-18 supported fiber optic probes.

Bacterial endotoxins such as lipopolysaccharides (LPS) are major contaminants of most pharmaceutical and consumer products. We report an antibiotic-mediated plasmonic biosensor for LPS detection based on a facile U-bent fiber optic probe (UFOP) technology. Biomimetic self-assembled layer of octadecyltrichlorosilanes (OTS) were functionalized on the surface of optical fiber probes to hydrophobically entrap LPS from aqueous solutions. The binding of LPS molecules was monitored in real-time by measuring the change in refractive index (RI) in the evanescent layer. To add specificity and signal amplification, the bound LPS molecules were further tagged with antimicrobial polymyxin-B conjugated gold nanoparticles (PMB-AuNPs) in a sandwich format. The assay was extensively optimized by investigating the role of experimental parameters like OTS concentration, incubation time and addition of a silver reduction step at the end of the assay. The lower limit of detection (LOD) for LPS was found to be 0.4 ng/mL with a 36-fold improved sensitivity upon silver enhancement. The total assay time was 1 h. The assay was also found to be highly specific in the presence of common biopharmaceutical components and could thus serve as an efficient endotoxin detection platform for quality control testing during therapeutic development.