The Determination of Methylmercury in Real Samples Using Organically Capped Mesoporous Inorganic Materials Capable of Signal Amplification

Recent Progress in External-Stimulus-Responsive 2D Covalent Organic Frameworks

Recently, smart 2D covalent organic frameworks (COFs), combining the advantages of both inherent structure features and functional building blocks, have been demonstrated to show reversible changes in conformation, color, and luminescence in response to external stimuli. This review provides a summary on the recent progress of 2D COFs that are responsive to external stimuli such as metal ions, gas molecules, pH values, temperature, electricity, light, etc. Moreover, the responsive mechanisms and design strategies, along with the applications of these stimulus-responsive 2D COFs in chemical sensors and photoelectronic devices are also discussed. It is believed that this review would provide some guidelines for designing novel single-/multistimulus-responsive 2D COFs with controllable responsive behaviors for advanced photoelectronic applications.

Development of a lateral flow test for rapid pyrethroid detection using antibody-gated indicator-releasing hybrid materials

The employment of type-I pyrethroids for airplane disinfection in recent years underlines the necessity to develop sensing schemes for the rapid detection of these pesticides directly at the point-of-use.

Overview of the Evolution of Silica-Based Chromo-Fluorogenic Nanosensors

This review includes examples of silica-based, chromo-fluorogenic nanosensors with the aim of illustrating the evolution of the discipline in recent decades through relevant research developed in our group. Examples have been grouped according to the sensing strategies. A clear evolution from simply functionalized materials to new protocols involving molecular gates and the use of highly selective biomolecules such as antibodies and oligonucleotides is reported. Some final examples related to the evolution of chromogenic arrays and the possible use of nanoparticles to communicate with other nanoparticles or cells are also included. A total of 64 articles have been summarized, highlighting different sensing mechanisms.

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.

New insights into the structure-performance relationships of mesoporous materials in analytical science

Mesoporous materials are ideal carriers for guest molecules and they have been widely used in analytical science. The unique mesoporous structure provides special properties including large specific surface area, tunable pore size, and excellent pore connectivity. The structural properties of mesoporous materials have been largely made use of to improve the performance of analytical methods. For instance, the large specific surface area of mesoporous materials can provide abundant active sites and increase the probability of contact between analytes and active sites to produce stronger signals, thus leading to the improvement of detection sensitivity. The connections between analytical performances and the structural properties of mesoporous materials have not been discussed previously. Understanding the "structure-performance relationship" is highly important for the development of analytical methods with excellent performance based on mesoporous materials. In this review, we discuss the structural properties of mesoporous materials that can be optimized to improve the analytical performance. The discussion is divided into five sections according to the analytical performances: (i) selectivity-related structural properties, (ii) sensitivity-related structural properties, (iii) response time-related structural properties, (iv) stability-related structural properties, and (v) recovery time-related structural properties.

Colorimetric detection of glucose using lanthanum-incorporated MCM-41

In this study, lanthanum-containing mesoporous MCM-41 (La-MCM-41) with different amount of lanthanum were synthesized and were used for colorimetric detection of glucose. As prepared La-MCM-41 were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The quantitative amounts of incorporated lanthanum into MCM-41 structure were estimated by energy dispersive X-ray spectrometry. The prepared La-MCM-41 provided high intrinsic peroxidase-like activity in the presence of peroxidise 3,3',5,5'-tetramethylbenzidine (TMB) and H₂O₂ for accurate determination of glucose. This process produced a blue color in aqueous solution that directly relates to H₂O₂ concentration. The effect of different parameters such as the content of incorporated lanthanum, pH, temperature and time of reaction on the peroxidase-like activity was studied. The colorimetric detection of H₂O₂ was led to a linear dynamic range from 50 to 1000 μM (r² = 0.9988) and low detection limit of 37.5 μM for glucose in aqueous solution. These results are comparable (close to) or better than some previous reports. Thus, La-MCM-41 can be used as admirable alternative design for colorimetric sensing of glucose.

NO2-controlled cargo delivery from gated silica mesoporous nanoparticles

Cargo delivery from mesoporous silica nanoparticles loaded with sulforhodamine B and capped with a difluoroboron-dipyrromethene (BODIPY) derivative was triggered by a NO₂-induced oxidative process.

Colorimetric Detection of Hg2+ Based on the Growth of Aptamer-Coated AuNPs: The Effect of Prolonging Aptamer Strands

Herein, a versatile and sensitive colorimetric sensor for Hg²⁺ based on aptamer-target specific binding and target-mediated growth of AuNPs is reported. The 15 T bases are first designed to detect Hg²⁺ through T-Hg²⁺ -T coordination. Aptamer-target binding results in the desorption of the aptamer from AuNP surface, the remaining aptamers adsorbed on AuNP surface trigger the growth of AuNPs with morphologically varied nanostructures, and then different colored solutions are formed. On this occasion, the limit of detection (LOD) of 9.6 × 10^-9 m is obtained. The other two aptamer strands (25- and 59-mer) are designed by increasing A bases on either side and both sides of 15 T, respectively. The interaction of the binding domain and Hg²⁺ makes desorption of 15 T from AuNP surface, whereas excess bases not committed to the binding domain still adsorbed on AuNP surface. These excess bases control the growth of AuNPs, and enhance the sensitivity. The LODs are 4.05 and 3 × 10^-9 m for 25- and 59-mer aptamers, respectively. In addition, the 59-mer aptamer system is applied to identify Hg²⁺ in real river samples, the LOD of 6.2 × 10^-9 m is obtained.

Pseudorotaxane capped mesoporous silica nanoparticles for 3,4-methylenedioxymethamphetamine (MDMA) detection in water

MDMA, a principal ecstasy component, is detected by using pseudorotaxane-capped mesoporous silica nanoparticles.

An electrochemically reduced graphene oxide chemiresistive sensor for sensitive detection of Hg2+ ion in water samples

Divalent mercuric (Hg²⁺) ion is one of the most prevalent forms of mercury species in waters with high toxicity and bioaccumulation in the human body, for which sensitive and selective detection methods are highly necessary to carry out its recognition and quantification. Here an electrochemically reduced graphene oxide (RGO) based chemiresistive sensor was constructed and used for the detection of Hg²⁺ ion in various water samples. Monolayer GO sheets were assembled onto interdigitated electrodes, followed by reduction through linear sweep voltammetry and then modification with a single-stranded DNA aptamer. The electrochemically derived RGO based sensor showed selective response to as low as 0.5nMHg²⁺ ion in presence of other metal ions and matrices. A comparison between chemiresistive sensors prepared with electrochemically and chemically derived RGO showed that the former had better response performance for sensing Hg²⁺ ion. The proposed method provides a simple tool for rapid, selective and sensitive monitoring of Hg²⁺ ion in environmental samples.

Self-Immolative Linkers as Caps for the Design of Gated Silica Mesoporous Supports

A new hybrid material based on sulforhodamine B dye-loaded silica mesoporous nanoparticles capped with a self-immolative gate has been synthesized and characterized. The gated material's controlled release behavior is monitored under different pH conditions. Under acidic and neutral conditions, a low level of dye release is detected. However, at slightly basic pH, significant dye release occurs owing to deprotonation of the phenol moiety in the capping molecule, which results in its disassembly.

A "Sense-and-Treat" Hydrogel Used for Treatment of Bacterial Infection on the Solid Matrix

A "sense-and-treat" hydrogel is constructed for sensing and inhibiting bacterial infection. Without bacteria, the hydrogel emits green fluorescence. With bacterial infection, the hydrogel emits red fluorescence and releases Vancomycin to kill bacteria.

A fluorescent probe for detection of an intracellular prognostic indicator in early-stage cancer

Cyclin A2 is a promising cancer prognostic indicator, but its intracellular in situ imaging is still a challenging task. This work designs an "off-on" fluorescent probe, which can fluorescently detect intracellular cyclin A2 and distinguish cancer cells. In addition, this work sheds light on the development of future protein biosensors.

Gated Silica Mesoporous Materials in Sensing Applications

Silica mesoporous supports (SMSs) have a large specific surface area and volume and are particularly exciting vehicles for delivery applications. Such container-like structures can be loaded with numerous different chemical substances, such as drugs and reporters. Gated systems also contain addressable functions at openings of voids, and cargo delivery can be controlled on-command using chemical, biochemical or physical stimuli. Many of these gated SMSs have been applied for drug delivery. However, fewer examples of their use in sensing protocols have been reported. The approach of applying SMSs in sensing uses another concept-that of loading pores with a reporter and designing a capping mechanism that is selectively opened in the presence of a target analyte, which results in the delivery of the reporter. According to this concept, we provide herein a complete compilation of published examples of probes based on the use of capped SMSs for sensing. Examples for the detection of anions, cations, small molecules and biomolecules are provided. The diverse range of gated silica mesoporous materials presented here highlights their usefulness in recognition protocols.

Chemical speciation of MeHg+ and Hg2+ in aqueous solution and HEK cells nuclei by means of DNA interacting fluorogenic probes

Selected new fluorogenic probes that interact in different ways with Hg2+ and MeHg+ have been prepared and used for the chemical speciation of both cations in aqueous solution as well as in HEK293 cells. The best selective speciation of Hg2+ and MeHg+ has been achieved by in vitro approaches based on fluorogenic probes supported in cultured cells, due to the particular sensitivity of the HEK293 cells to permeation by Hg2+, MeHg+ and the fluorogenic probes. In particular, MeHg+ was selectively detected in cell nuclei by probe JG45.

Gated mesoporous silica nanoparticles for the controlled delivery of drugs in cancer cells

In recent years, mesoporous silica nanoparticles (MSNs) have been used as effective supports for the development of controlled-release nanodevices that are able to act as multifunctional delivery platforms for the encapsulation of therapeutic agents, enhancing their bioavailability and overcoming common issues such as poor water solubility and poor stability of some drugs. In particular, redox-responsive delivery systems have attracted the attention of scientists because of the intracellular reductive environment related to a high concentration of glutathione (GSH). In this context, we describe herein the development of a GSH-responsive delivery system based on poly(ethylene glycol)- (PEG-) capped MSNs that are able to deliver safranin O and doxorubicin in a controlled manner. The results showed that the PEG-capped systems designed in this work can be maintained closed at low GSH concentrations, yet the cargo can be delivered when the concentration of GSH is increased. Moreover, the efficacy of the PEG-capped system in delivering the cytotoxic agent doxorubicin in cells was also demonstrated.

Silver nanoparticle gated, mesoporous silica coated gold nanorods (AuNR@MS@AgNPs): low premature release and multifunctional cancer theranostic platform

Multifunctional nanoparticles integrated with an imaging module and therapeutic drugs are promising candidates for future cancer diagnosis and therapy. Mesoporous silica coated gold nanorods (AuNR@MS) have emerged as a novel multifunctional cancer theranostic platform combining the large specific surface area of mesoporous silica, which guarantees a high drug payload, and the photothermal modality of AuNRs. However, premature release and side effects of exogenous stimulus still hinder the further application of AuNR@MS. To address these issues, herein, we proposed a glutathione (GSH)-responsive multifunctional AuNR@MS nanocarrier with in situ formed silver nanoparticles (AgNPs) as the capping agent. The inner AuNR core functions as a hyperthermia agent, while the outer mesoporous silica shell exhibits the potential to allow a high drug payload, thus posing itself as an effective drug carrier. With the incorporation of targeting aptamers, the constructed nanocarriers show drug release in accordance with an intracellular GSH level with maximum drug release into tumors and minimum systemic release in the blood. Meanwhile, the photothermal effect of the AuNRs upon application to near-infrared (NIR) light led to a rapid rise in the local temperature, resulting in an enhanced cell cytotoxicity. Such a versatile theranostic system as AuNR@MS@AgNPs is expected to have a wide biomedical application and may be particularly useful for cancer therapy.

A Chalcone-Based Highly Selective and Sensitive Chromofluorogenic Probe for Trivalent Metal Cations

A new chalcone-based probe for the chromofluorogenic sensing of trivalent (Al³⁺ , Fe³⁺ , Cr³⁺ , Ga³⁺ , In³⁺ and As³⁺ ) over mono- and divalent cations and anions is reported. In the presence of trivalent metal cations, the probe was able to display a remarkable color change from yellow to colorless that was clearly visible to the naked eye. Also, the initial strong yellow emission was gradually quenched and substituted by a weakly shifted band.

Ultrasensitive and highly selective detection of bioaccumulation of methyl-mercury in fish samples via Ag⁰/Hg⁰ amalgamation

Methylmercury (CH3Hg(+)), the common organic source of mercury, is well-known as one of the most toxic compounds that is more toxic than inorganic or elemental mercury. In seabeds, the deposited Hg(2+) ions are converted into CH3Hg(+) by bacteria, where they are subsequently consumed and bioaccumulated in the tissue of fish, and finally, to enter the human diet, causing severe health problems. Therefore, sensitive and selective detection of bioaccumulation of CH3Hg(+) in fish samples is desirable. However, selective assay of CH3Hg(+) in the mercury-containing samples has been seriously hampered by the difficulty to distinguish CH3Hg(+) from ionic mercury. We report here that metal amalgamation, a natural phenomenon occurring between mercury atoms and certain metal atoms, combining with DNA-protected silver nanoparticles, can be used to detect CH3Hg(+) with high sensitivity and superior selectivity over Hg(2+) and other heavy metals. In our proposed approach, discrimination between CH3Hg(+) and Hg(2+) ions was realized by forming Ag/Hg amalgam with a CH3Hg(+)-specific scaffold. We have found that Ag/Hg amalgam can be formed on a CH3Hg(+)-specific DNA template between silver atoms and mercury atoms but cannot between silver atoms and CH3Hg(+). With a dye-labeled DNA strand, the sensor can detect CH3Hg(+) down to the picomolar level, which is >125-fold sensitive over Hg(2+). Moreover, the presence of 50-fold Hg(2+) and 10(6)-fold other metal ions do not interfere with the CH3Hg(+) detection. The results shown herein have important implications for the fast, easy, and selective detection and monitoring of CH3Hg(+) in environmental and biological samples.

Assorted morphosynthesis: access to multi-faceted nano-architectures from a super-responsive dual π-functional amphiphilic construct

An electronically segmented amphiphile was created by conjugating two π-functional units (HQ/NDI) for the first time.

Highly selective and sensitive detection of glutathione using mesoporous silica nanoparticles capped with disulfide-containing oligo(ethylene glycol) chains

Mesoporous silica nanoparticles loaded with safranin O and capped with disulfide-containing oligo(ethylene glycol) chains were used for the selective and sensitive fluorimetric detection of glutathione.

Target-responsive DNA-capped nanocontainer used for fabricating universal detector and performing logic operations

Nucleic acids have become a powerful tool in nanotechnology because of their controllable diverse conformational transitions and adaptable higher-order nanostructure. Using single-stranded DNA probes as the pore-caps for various target recognition, here we present an ultrasensitive universal electrochemical detection system based on graphene and mesoporous silica, and achieve sensitivity with all of the major classes of analytes and simultaneously realize DNA logic gate operations. The concept is based on the locking of the pores and preventing the signal-reporter molecules from escape by target-induced the conformational change of the tailored DNA caps. The coupling of 'waking up' gatekeeper with highly specific biochemical recognition is an innovative strategy for the detection of various targets, able to compete with classical methods which need expensive instrumentation and sophisticated experimental operations. The present study has introduced a new electrochemical signal amplification concept and also adds a new dimension to the function of graphene-mesoporous materials hybrids as multifunctional nanoscale logic devices. More importantly, the development of this approach would spur further advances in important areas, such as point-of-care diagnostics or detection of specific biological contaminations, and hold promise for use in field analysis.

Thiol-addition reactions and their applications in thiol recognition

Because of the biological importance of thiols, the development of probes for thiols has been an active research area in recent years. In this review, we summarize the results of recent exciting reports regarding thiol-addition reactions and their applications in thiol recognition. The examples reported can be classified into four reaction types including 1,1, 1,2, 1,3, 1,4 addition reactions, according to their addition mechanisms, based on different Michael acceptors. In all cases, the reactions are coupled to color and/or emission changes, although some examples dealing with electrochemical recognition have also been included. The use of thiol-addition reactions is a very simple and straightforward procedure for the preparation of thiol-sensing probes.

Temperature-responsive DNA-gated nanocarriers for intracellular controlled release

We report a novel strategy to construct temperature-responsive nanocarriers for controlled release based on mesoporous silica and single-stranded DNA valves.

Luminescent carbon dot-gated nanovehicles for pH-triggered intracellular controlled release and imaging

In this paper, the use of biocompatible carbon dots (C-Dots) as caps on the surface of mesoporous silica nanoparticles (MSPs) for the design of intelligent on-demand molecular delivery and cell imaging system is described. These C-Dots-attached MSPs exhibited low cytotoxicity toward the cells and strong luminescence both in vitro and in vivo. A further loading of anticancer drug (DOX) endowed the fluorescent material with therapeutic functions. It was found that changing the pH to mildly acidic condition at physiological temperature caused the dissociation of the C-Dots@MSPs complex and release of a large number of DOX from the nanospheres. Moreover, the DOX-loaded nanocomposites exhibited a remarkably enhanced efficiency in killing cancer cells. The endocytosis and the efficient drug release properties of the system were confirmed by luminescence microscopy. Overall, we believe that the well-designed C-Dots@MSPs nanocomposites are promising for a simultaneous bioimaging and drug delivery system, which show more potential for clinical application.