Development of an Aptamer Based Luminescent Optical Fiber Sensor for the Continuous Monitoring of Hg2+ in Aqueous Media

Recent progress in nanomaterial-based aptamers as biosensors for point of care detection of Hg2+ ions and its environmental applications

Among the foremost persistent heavy metal ions in the ecosystem, mercury (Hg2+) remains intimidating to the environment by producing a catastrophic effect on the environment as well as on mankind due to the exacerbation of anthropogenic activities. Therefore, it has become necessary to develop superlative techniques for its detection even at low concentrations. The conventional approaches for Hg2+ ions are quite laborious, and expensive, and require expertise in operating sophisticated instruments. To overcome these limitations, aptamer-based biosensors emerged as a promising tool for its detection. DNA-based aptamers have evolved as a significant technique by detecting them even in ppb levels. This review outlines the progress in aptamer-based biosensors from the year 2019-2023 by inducing changes in the electrochemical signal or by fluorescent/colorimetric approaches. The electrochemical sensors used nanomaterial electrodes for increasing the sensitivity whereas fluorescent and colorimetric sensors exhibit quenching or strong fluorescence in the presence of Hg2+ ions depending upon the prevailing mechanism or visible color changes. This perturbation in the signals could be attributed to the formation of the T-Hg2+ -T complex with the aptamers in the presence of ions revealing its real-time and biological applications in living or cancerous cells. Furthermore, next-generation biosensors are suggested to bring a paradigm shift to the integration of high-end smartphones, machine learning, artificial intelligence, etc.

Glucose Oxidase Activity Colorimetric Assay Using Redox-Sensitive Electrochromic Nanoparticle-Functionalized Paper Sensors

Glucose oxidase (GOx) activity assays are vital for various applications, including glucose metabolism estimation and fungal testing. However, conventional methods involve time-consuming and complex procedures. In this study, we present a colorimetric platform for in situ GOx activity measurement utilizing redox-sensitive electrochromic nanoparticles based on polyaniline (PAni). The glucose-adsorbed colorimetric paper sensor, herein termed Glu@CPS, is created by immobilizing ferrocene and glucose onto paper substrates that have been functionalized with PAni nanoparticles. Glu@CPS not only demonstrated rapid detection (within 5 min) but also exhibited remarkable selectivity for GOx and a limit of detection as low as 1.25 μM. Moreover, Glu@CPS demonstrated consistent accuracy in the measurement of GOx activity, exhibiting no deviations even after being stored at ambient temperature for a duration of one month. To further corroborate the effectiveness of this method, we applied Glu@CPS in the detection of GOx activity in a moldy red wine. The results highlight the promising potential of Glu@CPS as a convenient and precise platform for GOx activity measurement in diverse applications including food quality control, environmental monitoring, and early detection of fungal contamination.

Recent Advances in the Application of Bionanosensors for the Analysis of Heavy Metals in Aquatic Environments

Heavy-metal ions (HMIs) as a pollutant, if not properly processed, used, and disposed of, will not only have an influence on the ecological environment but also pose significant health hazards to humans, making them a primary factor that endangers human health and harms the environment. Heavy metals come from a variety of sources, the most common of which are agriculture, industry, and sewerage. As a result, there is an urgent demand for portable, low-cost, and effective analytical tools. Bionanosensors have been rapidly developed in recent years due to their advantages of speed, mobility, and high sensitivity. To accomplish effective HMI pollution control, it is important not only to precisely pinpoint the source and content of pollution but also to perform real-time and speedy in situ detection of its composition. This study summarizes heavy-metal-ion (HMI) sensing research advances over the last five years (2019-2023), describing and analyzing major examples of electrochemical and optical bionanosensors for Hg2+, Cu2+, Pb2+, Cd2+, Cr6+, and Zn2+.

Ultrasensitive fluorescence sensor for Hg2+ in food based on three-dimensional upconversion nanoclusters and aptamer-modulated thymine-Hg2+-thymine strategy

Mercury (Hg²⁺) is a potentially toxic heavy metal ion found to be drastically deleterious to humans. Herein, an ultrasensitive fluorescence sensor was developed using three-dimensional upconversion nanoclusters (EBSUCNPs) and aptamer-modulated thymine-Hg²⁺-thymine strategy. The EBSUCNPs were used as the energy donors, the PDANPs served as the acceptors, and the aptamer was applied as an identification tag for Hg²⁺. Due to the energy transfer effect, the fluorescence of EBSUCNPs can be effectively quenched by Polydopamine nanoparticles (PDANPs). In the existence of Hg²⁺, T (thymine)-rich aptamers between EBSUCNPs and PDANPs were hybridized with Hg²⁺ to yield thymine-Hg²⁺-thymine and folded back to hairpin structure, causing PDANPs to detach from the EBSUCNPS and the recovery of fluorescence. Under optimum conditions, the linear sensing range of Hg²⁺ was 0.5-20 µg/L, and the detection limit was 0.28 µg/L. Furthermore, it exhibited excellent selectivity and anti-interference, which made it an ideal method for identifying Hg²⁺ in spiked samples.

Competitive fiber optic sensors for the highly selective detection of mercury in water

Two competitive fiber optic sensors for the rapid, sensitive, and highly selective detection of mercury in water are designed, fabricated, and evaluated. A wavelength-modulated sensor based on an etched single-mode-multimode-single-mode (E-SMS) optical fiber structure and an intensity-modulated sensor based on fiber optics with a slanted end were fabricated by readily reproducible methods. The sensors were activated with a nanostructured chitosan/maghemite (CS/Fe₂O₃) composite thin film for the selective detection of mercury ions (Hg²⁺) in water. The functionalized sensors were implemented to experimentally validate the potential of CS/Fe₂O₃ thin film for optical sensing of Hg²⁺ in drinking water. The sensor based on the E-SMS structure exhibited a wavelength-modulated response with a sensitivity of up to 290 pm/(µg/mL), and the sensor based on the slanted end structure showed an intensity-modulated response with a sensitivity of -0.07dBm/(µg/mL). Validation of the experimental assay method proves the ability to selectively detect chemical interactions as low as 1 ng/mL (one part per billion) of Hg²⁺ in water for both sensors. The high specificity of the two sensors was demonstrated by evaluating their responses to a number of potentially interfering metal ions in water. These sensors are cost-effective, simple to construct, and easy to implement, which makes them very promising for the on-site detection and monitoring of mercury in bodies of water.

Aptamer-based NanoBioSensors for seafood safety

Chemical and biological contaminants are of primary concern in ensuring seafood safety. Rapid detection of such contaminants is needed to keep us safe from being affected. For over three decades, immunoassay (IA) technology has been used for the detection of contaminants in seafood products. However, limitations inherent to antibody generation against small molecular targets that cannot elicit an immune response, along with the instability of antibodies under ambient conditions greatly limit their wider application for developing robust detection and monitoring tools, particularly for non-biomedical applications. As an alternative, aptamer-based biosensors (aptasensors) have emerged as a powerful yet robust analytical tool for the detection of a wide range of analytes. Due to the high specificity of aptamers in recognising targets ranging from small molecules to large proteins and even whole cells, these have been suggested to be viable molecular recognition elements (MREs) in the development of new diagnostic and biosensing tools for detecting a wide range of contaminants including heavy metals, antibiotics, pesticides, pathogens and biotoxins. In this review, we discuss the recent progress made in the field of aptasensors for detection of contaminants in seafood products with a view of effectively managing their potential human health hazards. A critical outlook is also provided to facilitate translation of aptasensors from academic laboratories to the mainstream seafood industry and consumer applications.

Differential Refractometric Biosensor for Reliable Human IgG Detection: Proof of Concept

A new sensing platform based on long-period fiber gratings (LPFGs) for direct, fast, and selective detection of human immunoglobulin G (IgG; Mw = 150 KDa) was developed and characterized. The transducer's high selectivity is based on the specific interaction of a molecularly imprinted polymer (MIPs) design for IgG detection. The sensing scheme is based on differential refractometric measurements, including a correction system based on a non-imprinted polymer (NIP)-coated LPFG, allowing reliable and more sensitive measurements, improving the rejection of false positives in around 30%. The molecular imprinted binding sites were performed on the surface of a LPFG with a sensitivity of about 130 nm/RIU and a FOM of 16 RIU^-1. The low-cost and easy to build device was tested in a working range from 1 to 100 nmol/L, revealing a limit of detection (LOD) and a sensitivity of 0.25 nmol/L (0.037 µg/mL) and 0.057 nm.L/nmol, respectively. The sensor also successfully differentiates the target analyte from the other abundant elements that are present in the human blood plasma.

Overview and emerging trends in optical fiber aptasensing

Optical fiber biosensors have attracted growing interest over the last decade and quickly became a key enabling technology, especially for the detection of biomarkers at extremely low concentrations and in small volumes. Among the many and recent fiber-optic sensing amenities, aptamers-based sensors have shown unequalled performances in terms of ease of production, specificity, and sensitivity. The immobilization of small and highly stable bioreceptors such as DNA has bolstered their use for the most varied applications e.g., medical diagnosis, food safety and environmental monitoring. This review highlights the recent advances in aptamer-based optical fiber biosensors. An in-depth analysis of the literature summarizes different fiber-optic structures and biochemical strategies for molecular detection and immobilization of receptors over diverse surfaces. In this review, we analyze the features offered by those sensors and discuss about the next challenges to be addressed. This overview investigates both biochemical and optical parameters, drawing the guiding lines for forthcoming innovations and prospects in this ever-growing field of research.

An overview of Structured Biosensors for Metal Ions Determination

The determination of metal ions is important for nutritional and toxicological assessment. Atomic spectrometric techniques are highly efficient for the determination of these species, but the high costs of acquisition and maintenance hinder the application of these techniques. Inexpensive alternatives for metallic element determination are based on dedicated biosensors. These devices mimic biological systems and convert biochemical processes into physical outputs and can be used for the sensitive and selective determination of chemical species such as cations. In this work, an overview of the proposed biosensors for metal ions determination was carried out considering the last 15 years of publications. Statistical data on the applications, response mechanisms, instrumentation designs, applications of nanomaterials, and multielement analysis are herein discussed.

Trends in the Design of Intensity-Based Optical Fiber Biosensors (2010-2020)

There exists an increasing interest in monitoring low concentrations of biochemical species, as they allow the early-stage detection of illnesses or the monitoring of the environment quality. Thus, both companies and research groups are focused on the development of accurate, fast and highly sensitive biosensors. Optical fiber sensors have been widely employed for these purposes because they provide several advantages for their use in point-of-care and real-time applications. In particular, this review is focused on optical fiber biosensors based on luminescence and absorption. Apart from the key parameters that determine the performance of a sensor (limit of detection, sensibility, cross-sensibility, etc.), other features are analyzed, such as the optical fiber dimensions, the sensing set ups and the fiber functionalization. The aim of this review is to have a comprehensive insight of the different aspects that must be taken into account when working with this kind of sensors.

Luminescent Cellulose Fibers Modified with Poly((9-Carbazolyl)Methylthiirane)

This article presents the results of research related to the development of cellulose man-made fibers with luminescent properties. The fibers were obtained from regenerated cellulose with the use of the N-Methylmorpholine-N-Oxide (NMMO) method for lyocell (Tencel) fiber formation. The method is named after the cellulose solvent (NMMO) used to obtain the spinning solution. Fibers are formed by the dry-wet spinning method. Due to the characteristic of the lyocell process, the fibers were easily modified to achieve luminescent properties with star-shaped organic compound poly((9-carbazolyl)methylthiirane) (KMT). Fibers were examined on their mechanical parameters with the use of Zwick Z2.5/TN1S tensile testing machine, and the results show the influence of the KMT concentration in the fiber matrix on mechanical parameters of the fibers. The study also attempted to determine the concentration of the modifier in the fibers with the use of UV-VIS Spectrofluorometer JASCO. The luminescent properties of fibers were estimated as well, using Jobin-Yvon spectrofluorometer FLUOROMAX-4, and the results are very promising as the fibers emit blue light in the range of visible light spectrum even for small concentrations of KMT (about 0.1 wt.%).