Nanoparticle stripe sensor for highly sensitive and selective detection of mercury ions

A novel 3D Zn-coordination polymer based on a multiresponsive fluorescent sensor demonstrating outstanding sensitivities and selectivities for the efficient detection of multiple analytes

A novel and unusual 3D luminescent coordination polymer (CP) [Zn₂(3-bpah)(bpta)(H₂O)]·3H₂O (1), where 3-bpah denotes N,N'-bis(3-pyridinecarboxamide)-1,2-cyclohexane and H₄bpta denotes 2,2',4,4'-biphenyltetracarboxylic acid, was successfully synthesized via hydrothermal methods from Zn(II) ions and 3-bpah and bpta ligands. The structure of this CP was investigated via powder X-ray diffraction (PXRD) analysis along with single crystal X-ray diffraction. Notably, 1 exhibits remarkable fluorescence behavior and stability over a wide pH range and in various pure organic solvents. More importantly, 1 can become an outstanding candidate for the selective and sensitive sensing of Fe³⁺, Mg²⁺, Cr₂O₇^2-, MnO₄^-, nitrobenzene (NB) and nitromethane (NM), at an extremely low detection limit. The changes in the fluorescence intensity exhibited by these six analytes in the presence of 1 over a wide pH range indicate that this polymer can be an excellent luminescent sensor. To the best of our knowledge, 1 is a rare example of a CP-based multiresponsive fluorescent sensor for metal cations, anions, and toxic organic solvents.

Trends in sensor development toward next-generation point-of-care testing for mercury

Mercury is one of the most common heavy metals and a major environmental pollutant that affects ecosystems. Since mercury and its compounds are toxic to humans, even at low concentrations, it is very important to monitor mercury contamination in water and foods. Although conventional mercury detection methods, including inductively coupled plasma mass spectrometry, atomic absorption spectroscopy, and gas chromatography-mass spectrometry, exhibit excellent sensitivity and accuracy, they require operation by an expert in a sophisticated and fully controlled laboratory environment. To overcome these limitations and realize point-of-care testing, many novel methods for direct sample analysis in the field have recently been developed by improving the speed and simplicity of detection. Commonly, these unconventional sensors rely on colorimetric, fluorescence, or electrochemical mechanisms to transduce signals from mercury. In the case of colorimetric and fluorescent sensors, benchtop methods have gradually evolved through technology convergence to give standalone platforms, such as paper-based assays and lab-on-a-chip systems, and portable measurement devices, such as smartphones. Electrochemical sensors that use screen-printed electrodes with carbon or metal nanomaterials or hybrid materials to improve sensitivity and stability also provide promising detection platforms. This review summarizes the current state of sensor platforms for the on-field detection of mercury with a focus on key features and recent developments. Furthermore, trends for next-generation mercury sensors are suggested based on a paradigm shift to the active integration of cutting-edge technologies, such as drones, systems based on artificial intelligence, machine learning, and three-dimensional printing, and high-quality smartphones.

Fabrication, calibration, and preliminary testing of microcantilever-based piezoresistive sensor for BioMEMS applications

In this study, the authors demonstrate the fabrication, calibration, and testing of a piezoresistive microcantilever-based sensor for biomedical microelectromechanical system (BioMEMS) application. To use any sensor in BioMEMS application requires surface modification to capture the targeted biomolecules. The surface alteration comprises self-assembled monolayer (SAM) formation on gold (Au)/chromium (Cr) thin films. So, the Au/Cr coating is essential for most of the BioMEMS applications. The fabricated sensor uses the piezoresistive technique to capture the targeted biomolecules with the SAM/Au/Cr layer on top of the silicon dioxide layer. The stiffness (k) of the cantilever-based biosensor is a crucial design parameter for the low-pressure range and also influence the sensitivity of the microelectromechanical system-based sensor. Based on the calibration data, the average stiffness of the fabricated microcantilever with and without Au/Cr thin film is 141.39 and 70.53 mN/m, respectively, which is well below the maximum preferred range of stiffness for BioMEMS applications. The fabricated sensor is ultra-sensitive and selective towards Hg²⁺ ions in the presence of other heavy metal ions (HMIs) and good enough to achieve a lower limit of detection 0.75 ng/ml (3.73 pM/ml).

Highly selective sensor for the detection of Hg2+ ions using homocysteine functionalised quartz crystal microbalance with cross-linked pyridinedicarboxylic acid

This study reports an insightful portable vector network analyser (VNA)-based measurement technique for quick and selective detection of Hg2+ ions in nanomolar (nM) range using homocysteine (HCys)-functionalised quartz-crystal-microbalance (QCM) with cross-linked-pyridinedicarboxylic acid (PDCA). The excessive exposure to mercury can cause damage to many human organs, such as the brain, lungs, stomach, and kidneys, etc. Hence, the authors have proposed a portable experimental platform capable of achieving the detection in 20-30 min with a limit of detection (LOD) 0.1 ppb (0.498 nM) and a better dynamic range (0.498 nM-6.74 mM), which perfectly describes its excellent performance over other reported techniques. The detection time for various laboratory-based techniques is generally 12-24 h. The proposed method used the benefits of thin-film, nanoparticles (NPs), and QCM-based technology to overcome the limitation of NPs-based technique and have LOD of 0.1 ppb (0.1 μg/l) for selective Hg2+ ions detection which is many times less than the World Health Organization limit of 6 μg/l. The main advantage of the proposed QCM-based platform is its portability, excellent repeatability, millilitre sample volume requirement, and easy process flow, which makes it suitable as an early warning system for selective detection of mercury ions without any costly measuring instruments.

Charged Metal Nanoparticles for Chemoelectronic Circuits

Although metal nanoparticles (NPs) stabilized with self-assembled monolayers (SAMs) of various organic ligands have proven useful in applications ranging from chemical sensing, to bionanotechnology, to plasmonics and energy conversion, they have not been widely considered as suitable building blocks of electronic circuitry, largely because metals screen electric fields and prevent electrically tunable conductivity. However, when metal nanoparticles a few nanometers in size are stabilized by charged ligands and placed under bias, the counterions surrounding the NPs can redistribute and establish local electric fields that feed back into the electronic currents passing through the nanoparticles' metallic cores. Herein, the manner in which the interplay between counterion gradients and electron flows can be controlled by using different types of SAMs is discussed. This can give rise to a new class of nanoparticle-based "chemoelectronic" logic circuits capable of sensing, processing, and ultimately reporting various chemical signals.

Re-designing ferritin nanocages for mercuric ion detection

Protein nanocages have recently received considerable attention in the fields of nanoscience and nanomedicine and have been used as either biotemplates for the preparation of a variety of nanomaterials or vehicles for drugs or imaging agents. However, their utilization for detection of heavy metal ions has yet to be explored. In this study, by grafting a mercury binding peptide (MBP) on the exterior surface of a recombinant human H-chain ferritin (rHuHF) nanocage, we successfully prepared a new protein nanocage (HuHF-MBP) which exhibits high binding capacity and affinity for Hg2+. The fluorescence of HuHF-MBP labeled with a green fluorescent dye fluorescein isothiocyanate (FITC) can be quenched by graphene oxide (GO), while addition of Hg2+ to the above solution recovered the quenched fluorescence in a dose-dependent manner. Thus, this system consisting of FITC-labeled HuHF-MBP and GO, where FITC and graphene oxide were used as fluorescent reporter probes, has great potential to be explored as a sensor for Hg2+ detection. Indeed, this newly constructed protein sensor exhibited high sensitivity and selectivity for Hg2+, and the limit of detection was 1.0 nM. The construction of this system provides an alternative strategy for the preparation of heavy metal ion sensors by using protein nanocages as biotemplates.

Isocyanonaphthalenes as extremely low molecular weight, selective, ratiometric fluorescent probes for Mercury(II)

The specially designed chemical structure of our recently developed solvatochromic amino-isocyanonaphthalene (ICAN) dye family enables the selective detection of Hg²⁺ and at the same time is able to indicate the presence of Ag⁺. In addition to its easy preparation and nontoxic nature, ICAN is the lowest molecular weight dye reported for ratiometric fluorescent Hg²⁺ detection in water, so far. The basis of this double selectivity is the reduction of the isonitrile moiety to amine by a chemical reaction with Hg²⁺ resulting in a greater than 100 nm hypsochromic shift (and switch on of fluorescence) of the emission maximum relative to ICAN, whereas the complexation of Ag⁺ with the NC group yields an approximately 20 nm bathochromic shift (and quenching). In contrast, other common ions have little effect on the position of the emission maximum in aqueous medium. In completely aqueous medium at pH = 6, the limit of quantification was found to be lower than 17 nM and the limit of detection lower than 6 nM for Hg²⁺. The practical applicability of the method was demonstrated on dental amalgam.

A compact prospective investigation on the colorimetric recognition of Hg2+ ion and photostimulated degradation of discharged toxic organic dyes motivated by H. mutabilis directed silver nanoparticles

A colorimetric sensing method for Hg²⁺ ion was developed using H. mutabilis motivated silver NPs. The calculated detection limit was estimated ∼48 pM. The nanoparticles also work as a good photo catalyst for degradation of TB and Rh-B.