An AIE fluorescent probe with a naphthalimide derivative and its application for detection of hypochlorite and imaging inside living cells

Hypochlorite (ClO^-) is a highly reactive oxygen species that plays an important role in resistance to attacks by microorganisms. Herein, we report the preparation of a fluorescence probe (NIB-M) through the integration of a naphthalimide moiety and ClO^- to capture diaminomaleonitrile and employ it for the aggregation-induced emission-based (AIE-based) monitoring of ClO^-. In the presence of ClO^-, NIB-M undergoes sequential nucleophilic substitution and HCl elimination reactions that allow it to possess high selectivity, a fast response, and a low detection limit (0.032 μM). Due to the good AIE properties of the parent molecule, a ClO^- test board was facilely prepared by loading NIB-M on a Whatman paper strip-based portable device. The test plate can conveniently and sensitively detect hypochlorite onsite. In addition, the NIB-M probe was used for the imaging of exogenous/endogenous ClO^- inside living cells.

Recent Advances in Electrochemical and Optical Sensing of Dopamine

Nowadays, several neurological disorders and neurocrine tumours are associated with dopamine (DA) concentrations in various biological fluids. Highly accurate and ultrasensitive detection of DA levels in different biological samples in real-time can change and improve the quality of a patient's life in addition to reducing the treatment cost. Therefore, the design and development of diagnostic tool for in vivo and in vitro monitoring of DA is of considerable clinical and pharmacological importance. In recent decades, a large number of techniques have been established for DA detection, including chromatography coupled to mass spectrometry, spectroscopic approaches, and electrochemical (EC) methods. These methods are effective, but most of them still have some drawbacks such as consuming time, effort, and money. Added to that, sometimes they need complex procedures to obtain good sensitivity and suffer from low selectivity due to interference from other biological species such as uric acid (UA) and ascorbic acid (AA). Advanced materials can offer remarkable opportunities to overcome drawbacks in conventional DA sensors. This review aims to explain challenges related to DA detection using different techniques, and to summarize and highlight recent advancements in materials used and approaches applied for several sensor surface modification for the monitoring of DA. Also, it focuses on the analytical features of the EC and optical-based sensing techniques available.

Fluorogenic Detection of Monoamine Neurotransmitters in Live Cells

Monoamine neurotransmission is key to neuromodulation, but imaging monoamines in live neurons has remained a challenge. Here we show that externally added ortho-phthalaldehyde (OPA) can permeate live cells and form bright fluorogenic adducts with intracellular monoamines (e.g., serotonin, dopamine, and norepinephrine) and with L-DOPA, which can be imaged sensitively using conventional single-photon excitation in a fluorescence microscope. The peak excitation and emission wavelengths (λ_ex = 401 nm and λ_em = 490 nm for serotonin; λ_ex = 446 nm and λ_em = 557 nm for dopamine; and λ_ex = 446 nm and λ_em = 544 nm for norepinephrine, respectively) are accessible to most modern confocal imaging instruments. The identity of monoamine containing structures (possibly neurotransmitter vesicles) in serotonergic RN46A cells is established by quasi-simultaneous imaging of serotonin using three-photon excitation microscopy. Mass spectrometry of cell extracts and of in vitro solutions helps us identify the chemical nature of the adducts and establishes the reaction mechanisms. Our method has low toxicity, high selectivity, and the ability to directly report the location and concentration of monoamines in live cells.

Cell-penetrating poly(disulfide)-based star polymers for simultaneous intracellular delivery of miRNAs and small molecule drugs

A cell-penetrating poly(disulfide)-based star-like system with high transfection efficacy for synergistic delivery of miRNAs and chemotherapeutic drugs has been reported.

An AIE-based fluorescent test strip for the portable detection of gaseous phosgene

An AIE-based ratiometric fluorescent test strip was developed for portable point-of-use detection of gaseous phosgene.

A highly selective and sensitive fluorescent nanosensor for dopamine based on formate bridged Tb(iii) complex and silver nanoparticles

The proposed fluorescent nanosensor can distinguish DA from EP.

Surface-functionalized hydrophilic monolayer of titanate and its application for dopamine detection

A surface-functionalized hydrophilic charge-neutral monolayer of titanate was exfoliated from the precursor layered composite in aqueous media without addition of a delamination agent. The hydrophilic monolayer was applied for the detection of dopamine based on visible-light absorption originating from charge-transfer excitation from adsorbed dopamine to titanate.

Simple and Sensitive Colorimetric Detection of Dopamine Based on Assembly of Cyclodextrin-Modified Au Nanoparticles

A controlled assembly of natural beta-cyclodextrin modified Au NPs mediated by dopamine is demonstrated. Furthermore, a simple and sensitive colorimetric detection for dopamine is established by the concentration-dependent assembly.

Paramagnetic relaxation based biosensor for selective dopamine detection

We report a new NMR relaxation time-based method for sensitive and selective dopamine detection using paramagnetic nanoparticles.

Anatase TiO2 based photoelectrochemical sensor for the sensitive determination of dopamine under visible light irradiation

The sensitive photoelectrochemical determination of dopamine was achieved using an indium tin oxide electrode modified with TiO₂ nanoparticles.

Molecular and supramolecular switches on mesoporous silica nanoparticles

This review summarizes the recent advances of molecular and supramolecular switches installed on mesoporous silica nanoparticles.

Terbium(iii)/gold nanocluster conjugates: the development of a novel ratiometric fluorescent probe for mercury(ii) and a paper-based visual sensor

A novel ratiometric fluorescent probe was developed for detection of mercury in rat tissues based on terbium(iii)/gold nanocluster conjugates. Meanwhile, a paper-based visual sensor for detection of Hg²⁺ with the naked eye was designed.

Selective dopamine chemosensing using silver-enhanced fluorescence

Condensation product of salicylaldehyde and 1,3 propylenediamine becomes a diiminic Schiff base, which is oxidized by AgNO3 in alkaline solution, and in turn, stable Ag(0) is produced at room temperature. Under this condition, the solution exhibits intense silver nanoparticle enhanced fluorescence (SEF) with the λ(em) at 412 nm. Dopamine is selectively detected down to the nanomolar level via exclusive fluorescence quenching of the SEF. Dopamine-infested solution regains the fluorescence [i.e., SEF in the presence of Hg(II) ions]. Thus dopamine and Hg(II) in succession demonstrate "turn off/on" fluorescence due to the change in the scattering cross section of Ag(0) and gives a quantitative measure of dopamine in real samples. The proposed method is free from interferences of common biocompetitors.

pH and ion strength modulated ionic species loading in mesoporous silica nanoparticles

Mesoporous silica nanoparticles (MSN) have emerged as appealing host materials to accommodate guest molecules for biomedical applications, and recently various methods have been developed to modulate the loading of guest molecules in the silica matrix. Herein, it was demonstrated that pH and ion strength showed great influence on the loading of charged species into the nanoparticles, taking MCM-41 as a host MSN model and methylviologen (MV(2+)) and 1,5-naphthalene disulfonate (NDS(2-)) as typical charged ionic guest molecules. As the pH increased from 3.0 to 8.0, the loading amount of MV(2+) increased gradually, while on the contrary, it decreased gradually for NDS(2-), for the solution pH changed the electrostatic interaction between the silica matrix and the ionic guest molecules. Additionally, the adding of NaCl reduced the electrostatic interaction, which resulted in a decreasing of the electrostatic rejection and electrostatic accumulation for the molecules carrying the same and the opposite charge to the particle respectively. Thus, pH and ion strength can be employed as simple approaches to modulate the loading of charged molecules and permselectivity in MSN. This work has a definite guidance function for molecule loading, transport modulation, controlled release as well as sensors based on MSN.

An enzyme-responsive nanocontainer as an intelligent signal-amplification platform for a multiple proteases assay

Based on selective pore-opening in the presence of protease, we have developed a novel signal amplification assay for multiple proteases detection and their inhibition using protein-capped mesoporous scaffolding as the substrate.

Indium tin oxide-coated glass modified with reduced graphene oxide sheets and gold nanoparticles as disposable working electrodes for dopamine sensing in meat samples

Sensitive, rapid, and accurate detection of dopamine (DA) at low cost is needed for clinical diagnostic and therapeutic purposes as well as to prevent illegal use of DA in animal feed. We employed a simple approach to synthesize reduced graphene oxide sheets (rGOS) and gold nanoparticles (AuNPs) at room temperature on indium tin oxide-coated glass (ITO) slides as disposable working electrodes for sensing DA. Graphene oxide (GO) was directly reduced on ITO to remove oxygenated species via a rapid and green process without using chemical reducing reagents. AuNPs were electrochemically deposited in situ on rGOS-ITO with fairly uniform density and size. The sensitivity of the AuNPs-rGOS-ITO sensor for DA detection is 62.7 μA mM(-1) cm(-2) with good selectivity against common electrochemically interfering species such as ascorbic acid (AA) and uric acid (UA), and the detection limit measured by differential pulse voltammetry (DPV), at a signal-noise ratio of 3, was 6.0 × 10(-8) M. The electrochemical catalysis of DA was proven to be a surface process with an electron transfer coefficient (α) of 0.478 and a rate constant (k(s)) of 1.456 s(-1). It correlates well with the conventional UV-vis spectrophotometric approach (R = 0.9973) but with more than thrice the dynamic range (up to 4.5 mM). The sensor also exhibited good stability and capability to detect DA in beef samples, and thus is a promising candidate for simple and inexpensive sub-nanomolar detection of DA, especially in the presence of UV-absorbing compounds.

A silica nanoparticle-based sensor for selective fluorescent detection of homocysteine via interaction differences between thiols and particle-surface-bound polymers

Biothiols play crucial roles in maintaining biological systems; among them, homocysteine (Hcy) has received increasing attention since elevated levels of Hcy have been implicated as an independent risk factor for cardiovascular disease. Hence, the selective detection of this specific biothiol, which is a disease-associated biomarker, is very important. In this paper, we demonstrate a new mesoporous silica nanoparticle-based sensor for selective detection of homocysteine from biothiols and other common amino acids. In this fluorescent sensing system, an anthracene nitroolefin compound was placed inside the mesopores of mesoporous silica nanoparticles (MSNs) and used as a probe for thiols. The hydrophilic polyethylene glycol (PEG 5000) molecules were covalently bound to the MSN surface and used as a selective barrier for Hcy detection via different interactions between biothiols and the PEG polymer chains. The sensor can discriminate Hcy from the two low-molecular mass biothiols (GSH and Cys) and other common amino acids in totally aqueous media as well as in serum, with a detection limit of 0.1 μM. This strategy may offer an approach for designing other MSN-based sensing systems by using polymers as diffusion regulators in sensing assays for other analytes.