Selective detection of manganese(II) ions based on the fluorescence turn-on response via histidine functionalized carbon quantum dots

Herein, water-soluble emissive carbon quantum dots (His-CQDs) were synthesized from pyrolysis of sodium citrate in the presence of histidine under hydrothermal conditions. The as-synthesized His-CQDs were characterized using Fourier transform infrared (FT-IR), fluorescence spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM) techniques. The obtained His-CQDs display a strong emission peak at 534 nm when excited at 476 nm with a high quantum yield (61.8 %). The as-synthesized His-CQDs were applied as a new platform for highly selective determination of Mn(II) based on the fluorescence "turn-on" response with a limit of detection of 1.85 µg L^-1 (at 3σ) and a linear range of 3.50-35.5 µg L^-1 in aqueous solution. The sensing mechanism of the His-CQDs probe for the detection of Mn(II) was studied via density functional theory (DFT), FT-IR, and EDTA complexation methodology. In addition, His-CQDs were successfully applied to determine the accurate amounts of Mn(II) in whole blood control material. More importantly, the integrating such an efficient sensor with point-of-care technology can enable portable, easy-to-use, and rapid sensing systems for better biological and clinical applications.

Tuning optical properties and optical rotation of 3-mercaptopropionic acid capped organic-inorganic hybrid perovskites

The emission wavelength of organic-inorganic hybrid perovskite quantum dots (QDs) can be tuned by controlling reaction time relevant to the halide exchange. It is because halide exchange with different time would lead to different molar ratio of halides in perovskite QDs such as Cl and Br. Here, to research the ligand's effect on the halide exchange, this work synthesized 3-mercaptopropionic acid (MPA)-capped CH₃ NH₃ PbBr_x Cl_3-x QDs. It was found that SH^- of MPA appeared to inhibit the halide exchange during the reation. Moreover, although the MPA-capped CH₃ NH₃ PbBr_x Cl_3-x QDs did not contain the chiral centre, they exhibit the optical rotation. This may provide a method for chirality manipulation of perovskite.

Potentially toxic elements and environmentally-related pollutants recognition using colorimetric and ratiometric fluorescent probes

A safer detection or sensing of toxic pollutants is one among several environmental contamination issues, across the globe. The ever-increasing industrial practices and controlled or uncontrolled release of toxic pollutants from various industrial sectors is a key source of this environmental problem. Significant research efforts have been or being made to tackle this problematic issue to fulfill the growing needs of the modern world. Despite many useful aspects, heavy metals are posing noteworthy toxicological concerns and human-health related issues at various levels of the ecosystem. In this context, notable efforts from various regulatory authorities, the increase in the concentration of these toxic heavy metals in the environment is of serious concern, so real-time monitoring is urgently required. Herein, we reviewed fluorescent sensor based models and their potentialities to address the detection fate of hazardous pollutants including chromium, manganese, cobalt, nickel, copper, and zinc as model elements. The novel aspects of turn-on/off fluorescent sensors have also been discussed from a state of the art viewpoint. In summary, comprehensive literature regarding fluorescent sensor based models and their potentialities to detect various types of toxic pollutants is reviewed.

Synthesis and Properties of Water-Soluble Blue-Emitting Mn-Alloyed CdTe Quantum Dots

In this work, we prepared CdTe quantum dots, and series of Cd_1-xMn_xTe-alloyed quantum dots with narrow size distribution by an ion-exchange reaction in water solution. We found that the photoluminescence peaks are shifted to higher energies with the increasing Mn²⁺ content. So far, this is the first report of blue-emitting CdTe-based quantum dots. By means of cyclic voltammetry, we detected features of electrochemical activity of manganese energy levels formed inside the Cd_1-xMn_xTe-alloyed quantum dot band gap. This allowed us to estimate their energy position. We also demonstrate paramagnetic behavior for Cd_1-xMn_xTe-alloyed quantum dots which confirmed the successful ion-exchange reaction.

Distinction between Mn(iii) and Mn(ii) by using a colorimetric chemosensor in aqueous solution

A new colorimetric chemosensor for Mn(iii) and Mn(ii) was developed and used to differentiate between Mn(iii) and Mn(ii).

Fluorescent, MRI, and colorimetric chemical sensors for the first-row d-block metal ions

Transition metals (d-blocks) are recognized as playing critical roles in biology, and they most often act as cofactors in diverse enzymes; however, improper regulation of transition metal stores is also connected to serious disorders. Therefore, the monitoring and imaging of transition metals are significant for biological research as well as clinical diagnosis. In this article, efforts have been made to review the chemical sensors that have been developed for the detection of the first-row d-block metals (except Cu and Zn): Cr, Mn, Fe, Co, and Ni. We focus on the development of fluorescent sensors (fall into three classes: "turn-off", "turn-on", and ratiometric), colorimetric sensors, and responsive MRI contrast agents for these transition metals (242 references). Future work will be likely to fill in the blanks: (1) sensors for Sc, Ti, and V; (2) MRI sensors for Cr, Mn, Co, Ni; (3) ratiometric fluorescent sensors for Cr(6+), Mn(2+), and Ni(2+), explore new ways of sensing Fe(3+) or Cr(3+) without the proton interference, as well as extend applications of MRI sensors to living systems.

Discriminative detection of bivalent Cu by dual-emission ZnSe quantum dot fluorescence sensing via ratiometric fluorescence measurements

In this work, we showed that 1-thioglycerol (TG)-capped ZnSe quantum dots (QDs) with dual-emission could perform ideal QD fluorescence sensing for ratiometric fluorescence measurements. By comparing the fluorescence ratios at two emission peaks before and after the addition of cations, the discriminative detection of Cu(II) was realized, even in the case of co-existing with large amounts of other sensitive cations, such as Ag(I). The discriminative detection of Cu(II) is accurate with co-existing Ag(I) below 10 μmol L(-1). By a joint investigation of the ionic diffuse dynamics and carrier recombination dynamics, we found that the adsorbed layer of QDs plays a key role in the discriminative detection of Cu(II) from Ag(I) or other sensitive cations. The moderate adsorption capacity with a QD adsorbed layer makes Cu(II) capable of travelling across the QD double-layer structure, following a surface doping process via chemical reactions between Cu(II) and the QD surface atoms. As a result of Cu(II) doping, there were three major carrier recombination channels: the non-radiation recombination between the QD conduction band to the Cu(II) energy level, together with the non-radiation recombination and radiation recombination between the trap state energy levels and the Cu(II) energy level. As for Ag(I) and other sensitive cations, they have a strong adsorption capacity with the QD adsorbed layer, making them mainly present on the adsorbed layer. Due to the blocking of the ligand layer, we only observed weak coupling of the ZnSe conduction band with the Ag(I) energy level via a non-radiation recombination channel.

Semicondutor quantum dots-based metal ion probes

Semiconductor quantum dots (QDs) exhibit unique optical and photophysical properties that offer significant advantages over organic dyes as optical labels for chemo/bio-sensing. This review addresses the methods for metal ion detection with QDs, including photoluminescent, electrochemiluminescent, photoelectrochemical, and electrochemical approaches. The main mechanisms of direct interaction between QDs and metal ions which lead to photoluminescence being either off or on, are discussed in detail. These direct interactions provide great opportunities for developing simple yet effect metal ion probes. Different methods to design the chemically-modified QD hybrid structures through anchoring metal ion-specific groups onto the surface of QDs are summarized. Due to the spatial separation of the luminescence center and analyte recognition sites, these chemically-modified QDs offer greatly improved sensitivity and selectivity for metal ions. Several interesting applications of QD-based metal ion probes are presented, with specific emphasis on cellular probes, coding probes and sensing with logic gate operations.

A highly sensitive and selective colorimetric sensor for the detection of Mn2+ based on supramolecular silver nanoparticle clusters

A colorimetric sensor decorated with β-cyclodextrin and adamantine has been designed to enhance the sensitivity of Mn²⁺ detection.

Colloidal semiconductor nanocrystals: the aqueous approach

This article summarizes the main achievements and challenges in the field of the aqueous synthesis of semiconductor quantum dots in colloidal solutions. Developments in the last two decades demonstrate the great potential of this approach to synthesize nanocrystalline materials with superior properties such as strong photoluminescence, long time stability and compatibility with biological media, and the variability in assembling and self-assembling into larger structures or on surfaces. Being relatively straightforward, the aqueous approach provides some advantages such as versatility, scalability, environmental friendliness and cost effectiveness, leading in summary to very attractive application perspectives.

Bipyrene-functionalized graphene as a "turn-on" fluorescence sensor for manganese(II) ions in living cells

1,2-bis-(2-pyren-1-ylmethylamino-ethoxy) ethane (NPEY) was synthesized and brought to the surface of graphene nanosheets (GNs) via π-π stacking, which provided a simple and convenient route for processing "turn-on" fluorescent sensor by simply mixing the diluted aqueous solutions of both components. The synthesized NPEY modified graphene nanosheets (NPEY-GNs) not only allows good selectivity toward Mn(2+) with the detection limit of 4.6 × 10(-5) M, but also shows "turn-on" response for Mn(2+) both in vitro and in living cells. These sensing capabilities of NPEY-GNs in living cells make it a robust candidate for many biological fields, such as intracellular tracking, intracellular imaging, etc.