Selective fluorimetric detection of cadmium in a microfluidic device

Trace detection of cadmium (II) ions based on an excessively tilted fiber grating

Cadmium (Cd2+) ion is one of the most crucial industrial pollutants that cause serious harm to the human body. We proposed and experimentally demonstrated a highly sensitive Cd2+ sensor based on hydrogel coated excessively tilted fiber grating. The hydrogel with the functional monomer of the allyl thiourea can specifically bind to Cd2+, and hence forming a complex. The grating excites high order cladding modes, and ensures a sufficient interaction between the light and hydrogel binding to Cd2+, providing highly sensitive monitoring. The results show that the sensor can detect 0-160 pM Cd2+ in aqueous solution. The maximum sensitivity is 10600 nm/µM, and the minimum detection concentration is 20 pM (about 0.004 ppb), which is much less than that of the international standard (3 ppb). The proposed sensor exhibits high sensitivity, ultra-low detection limit, specificity, and a compact structure, offering potential as a tool for Cd2+ detection in aqueous solution.

Microfluidic Devices for Heavy Metal Ions Detection: A Review

The contamination of air, water and soil by heavy metal ions is one of the most serious problems plaguing the environment. These metal ions are characterized by a low biodegradability and high chemical stability and can affect humans and animals, causing severe diseases. In addition to the typical analysis methods, i.e., liquid chromatography (LC) or spectrometric methods (i.e., atomic absorption spectroscopy, AAS), there is a need for the development of inexpensive, easy-to-use, sensitive and portable devices for the detection of heavy metal ions at the point of interest. To this direction, microfluidic and lab-on-chip (LOC) devices fabricated with novel materials and scalable microfabrication methods have been proposed as a promising approach to realize such systems. This review focuses on the recent advances of such devices used for the detection of the most important toxic metal ions, namely, lead (Pb), mercury (Hg), arsenic (As), cadmium (Cd) and chromium (Cr) ions. Particular emphasis is given to the materials, the fabrication methods and the detection methods proposed for the realization of such devices in order to provide a complete overview of the existing technology advances as well as the limitations and the challenges that should be addressed in order to improve the commercial uptake of microfluidic and LOC devices in environmental monitoring applications.

FeOOH nanosheet assisted metal ion coordination with porphyrins for rapid detection and removal of cadmium ions in water

Excessive cadmium ions in water bodies pose a severe challenge to ecology and human health, and the development of cadmium metal ion sensors is imperative. Here, we showed a dual-signal sensor based on colorimetry and fluorescence that was self-assembled from FeOOH nanosheets and TMPyP4. This nanocomposite enabled quick, selective cadmium ion detection. The Soret band at 442 nm in the UV absorption spectrum represented the coordination of cadmium ions with FeOOH@TMPyP4, and the absorbance increased linearly with increasing cadmium ion concentration (R² = 0.989 and linear range: 0.5-10 μM). In the presence of FeOOH nanosheets, the coordination of cadmium ions with FeOOH@TMPyP4 took only 70 min, and the detection limit of cadmium ions was as low as 0.24 μM. In addition, Cd²⁺ could be effectively removed from the nanocomposite due to its easy separation from water. This research developed a simple and efficient approach for detecting and removing heavy metal ions from water bodies.

Cadmium Ions' Trace-Level Detection Using a Portable Fiber Optic-Surface Plasmon Resonance Sensor

Environmental pollution with cadmium (Cd) is a major concern worldwide, with prolonged exposure to this toxic heavy metal causing serious health problems, such as kidney damage, cancer, or cardiovascular diseases, only to mention a few. Herein, a gold-coated reflection-type fiber optic--surface plasmon resonance (Au-coated FO-SPR) sensor is manufactured and functionalized with (i) bovine serum albumin (BSA), (ii) chitosan, and (iii) polyaniline (PANI), respectively, for the sensitive detection of cadmium ions (Cd2+) in water. Then, the three sensor functionalization strategies are evaluated and compared one at a time. Out of these strategies, the BSA-functionalized FO-SPR sensor is found to be highly sensitive, exhibiting a limit of detection (LOD) for Cd2+ detection at nM level. Moreover, the presence of Cd2+ on the FO-SPR sensor surface was confirmed by the X-ray photoelectron spectroscopy (XPS) technique and also quantified consecutively for all the above-mentioned functionalization strategies. Hence, the BSA-functionalized FO-SPR sensor is sensitive, provides a rapid detection time, and is cheap and portable, with potential applicability for monitoring trace-level amounts of Cd within environmental or potable water.

A Review of Microfluidic Detection Strategies for Heavy Metals in Water

Heavy metal pollution of water has become a global issue and is especially problematic in some developing countries. Heavy metals are toxic to living organisms, even at very low concentrations. Therefore, effective and reliable heavy metal detection in environmental water is very important. Current laboratory-based methods used for analysis of heavy metals in water require sophisticated instrumentation and highly trained technicians, making them unsuitable for routine heavy metal monitoring in the environment. Consequently, there is a growing demand for autonomous detection systems that could perform in situ or point-of-use measurements. Microfluidic detection systems, which are defined by their small size, have many characteristics that make them suitable for environmental analysis. Some of these advantages include portability, high sample throughput, reduced reagent consumption and waste generation, and reduced production cost. This review focusses on developments in the application of microfluidic detection systems to heavy metal detection in water. Microfluidic detection strategies based on optical techniques, electrochemical techniques, and quartz crystal microbalance are discussed.

Selective detection of cadmium ions using plasmonic optical fiber gratings functionalized with bacteria

Environmental monitoring and potable water control are key applications where optical fiber sensing solutions can outperform other technologies. In this work, we report a highly sensitive plasmonic fiber-optic probe that has been developed to determine the concentration of cadmium ions (Cd²⁺) in solution. This original sensor was fabricated by immobilizing the Acinetobacter sp. around gold-coated tilted fiber Bragg gratings (TFBGs). To this aim, the immobilization conditions of bacteria on the gold-coated optical fiber surface were first experimentally determined. Then, the coated sensors were tested in vitro. The relative intensity of the sensor response experienced a change of 1.1 dB for a Cd²⁺ concentration increase from 0.1 to 1000 ppb. According to our test procedure, we estimate the experimental limit of detection to be close to 1 ppb. Cadmium ions strongly bind to the sensing surface, so the sensor exhibits a much higher sensitivity to Cd²⁺ than to other heavy metal ions such as Pb²⁺, Zn²⁺ and CrO₄^2- found in contaminated water, which ensures a good selectivity.

Autonomous and In Situ Ocean Environmental Monitoring on Optofluidic Platform

Determining the distributions and variations of chemical elements in oceans has significant meanings for understanding the biogeochemical cycles, evaluating seawater pollution, and forecasting the occurrence of marine disasters. The primary chemical parameters of ocean monitoring include nutrients, pH, dissolved oxygen (DO), and heavy metals. At present, ocean monitoring mainly relies on laboratory analysis, which is hindered in applications due to its large size, high power consumption, and low representative and time-sensitive detection results. By integrating photonics and microfluidics into one chip, optofluidics brings new opportunities to develop portable microsystems for ocean monitoring. Optofluidic platforms have advantages in respect of size, cost, timeliness, and parallel processing of samples compared with traditional instruments. This review describes the applications of optofluidic platforms on autonomous and in situ ocean environmental monitoring, with an emphasis on their principles, sensing properties, advantages, and disadvantages. Predictably, autonomous and in situ systems based on optofluidic platforms will have important applications in ocean environmental monitoring.

Water-soluble aluminium fluorescent sensor based on aggregation-induced emission enhancement

Development of a portable miniature system for Al(iii) detection in pure aqueous solutions using a novel AIEE compound.

MoS2-Nanosheet-Assisted Coordination of Metal Ions with Porphyrin for Rapid Detection and Removal of Cadmium Ions in Aqueous Media

Molybdenum disulfide (MoS₂) is a two-dimensional (2D) graphene-like material that is gaining great attention because of its potential application in various fields. Here, we reported a self-assembled nanocomposite consisted of MoS₂ nanosheets and 5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrintetra(p-toluenesulfonate) (TMPyP), named MoS₂@TMPyP. This nanocomposite can be used as a sensing probe for low cost, rapid, selective detection of cadmium (Cd²⁺) ions. It is found that a new Soret band at 442 nm in UV-vis absorption spectra represented the coordination of Cd²⁺ ions into TMPyP of the MoS₂@TMPyP. The coordination rates between TMPyP and Cd²⁺ ions is greatly accelerated from 72 h to 20 min with the assistance of MoS₂, which is 200 times faster than in the absence of MoS₂. The limit of detection (LOD) of the Cd²⁺ is as low as 7.2 × 10^-8 mol/L. The binding behavior between the cationic TMPyP and MoS₂ nanosheets was corroborated by molecular dynamics simulation and various control experiments. The results demonstrated that electrostatic interaction was the main force for driving TMPyP enriching around the MoS₂ surface, resulting in an accelerated complexation of Cd²⁺ and TMPyP. Moreover, MoS₂@TMPyP nanocomposite can also be used for removing of Cd²⁺ in water. The removal efficiency (RF) of the MoS₂@TMPyP can reach to 91% for high concentrations of Cd²⁺. This work provides a new insight into detection and removal of Cd²⁺ ions in water.

New sensitive and selective calixarene-based fluorescent sensors for the detection of Cs+ in an organoaqueous medium

A calixarene-based fluorescent sensor has been designed for the detection of Cs⁺ in the micromolar range.

Selective, direct detection of acetylcholine in PBS solution, with self-assembled fluorescent nano-particles: experiment and modelling

Self-assembled nano-particles of a new cyclotriveratrylene discriminate acetylcholine from choline in physiological buffer solution.

Recent progress in optical chemical sensors

Optical chemical sensors have promoted escalating interest in the determination of various pollutants in the environment, which are creating toxicity and may cause serious health problems. This review paper focuses particularly on the recent progress and developments in this field; the working principles and basic classes of optical chemical sensors have been briefly described.