Fluorescence Sensors

Phthalocyanine tetrasulfonic acid (PCTS) performed as a optical probe for selective detection of Cu 2+ in DMSO solution over other metal ions used. The complexation behavior of chemodosimeter toward various metal ions has been studied via UV-vis absorption and fluorescence emission spectra. Induced changes were found to be observable from naked eye. The association constant (K a ) and low limit of detection were found to be 8.80 × 10 5 M −1 and 5.53 × 10 −7 M, respectively. The optode showed excellent selectivity behavior in the environmental pH range.

A new rhodamine-derived Schiff base RH was synthesized and its sensing behavior toward various metal ions was investigated by UV–vis and fluorescence spectroscopic techniques. The sensor exhibited highly selective and sensitive colorimetric response to Cu 2+ and Al 3+ , and " off–on " fluorescence response toward Fe 3+ in semi-aqueous media. The spectral changes obtained are large enough in the visible region of the spectrum and thus enable naked-eye detection. Experimentally proved that the formation of RH–Al 3+ complex is fully reversible and can sense to AcO − /F − via break the complex. The results revealed that the sensor offers the sequential detection of Al 3+ and AcO − /F − .

Two new highly selective colorimetric and fluoregenic aminopyridine Schiff bases (L1 and L2) were synthesized by simple refluxing method and characterised via standard NMR and HRMS techniques. Its excellent metal sensing abilities explored on absorbance and fluorescence spectroscopy. The recognition colorimertric sensing behavior of probes L1 and L2 towards Ni(II), Zn(II), Fe(III) and UO 2 (II) ions were carefully investigated with different aspects of sensing behavior such as sensitivity, binding constant , stoichiometry, pH range and interference effect. Moreover, L1 and L2 also displayed excellent " off-on " fluoregenic selectivity with Zn(II). The results revealed that the sensors provided colorimetric and fluoregenic sensing excellent response with low limit of detection, under neutral conditions.

Anion sensing behaviour of a quinoline-based derivative has been explored and is found to be selective towards HSO 4 À over a variety of anions including oxo anions. The sensing protocol has been suggested to proceed via a static emission quenching process which has further been supported by 1 H NMR, UV-vis and theoretical (DFT, TD-DFT) calculations indicating the formation of a hydrogen-bonded complex between the quinoline part of the receptor and HSO 4 À . † Electronic supplementary information (ESI) available: Synthetic procedure, characterization/spectral data of 1, calculation of quantum yield, Gaussian optimized structure of 1, uorescence spectra, UV-vis and TD-DFT data. See

A novel fluorescent boronate nanoprobe has been synthesized by judiciously doping boron, nitrogen, and sulphur in carbon quantum dots (BNSCQD). Specifically, the synergistic presence of nitrogen and sulphur along with boronic acid provides excellent luminescence properties and offers recognition sites for specific sensing of glucosamine. Fluorescence intensity enhances in the presence of glucosamine because of agglomeration of luminescent centers, and thus restricts nonradiative emission channels. The detection limit of this turn on fluorescence for glucosamine is 0.7 nM in PBS. Following this protocol, for the first time, a paper based sensor strip has been prepared for naked eye detection of glucosamine with an LOD of 2.5 mM. The developed nanoprobe shows very low cytotoxicity. More interestingly, boronic acid located on the surface of BNSCQD offers molecular recognition sites for the sialyl Lewis a receptor, which is overexpressed on the surface of liver cancer cells (HepG2). The selective uptake of the BNSCQD nanoprobe in HepG2 cells compared to L929, 3T3 and PC3 cells shows its cell targeting capability. Fluorescence sensing has been emerging as an efficient detection method because of its high sensitivity and spatiotemporal resolution. 1-5 The effectiveness of boronic acid as a receptor in chemosensors for a wide range of biologically important species has been extensively reported. The reversible covalent interaction of boronic acid with cis 1,2 or 1,3 diols to form five or six membered cyclic esters, respectively, has proven to be sufficiently strong and enables the binding of saccharides at mM or sub mM levels. 6,7 Based on this binding principle, a number of fluorescence sensors have been designed for detecting sugars, 8,9 aminosugars, 10,11 cell surface glycans, 12-14 etc. However, organic fluorescence sensors are expensive, involve a multistep synthesis process and are normally unworthy for practical promotion and application. By virtue of favorable optical properties and surface functionality, carbon nanomaterial-based sensing systems have been successfully applied for glucose sensing. 15 For instance, Qiu et al. have reported a fluorescence sensor constituting a combination of anionic graphene quantum dots and bipyridinum salts for detection of sugars and other saccharides. 16 This method offers a simple mix-and-detect protocol for rapid detection of glucose and other saccharides, but it lacks selectivity. Later, two different protocols were published where boronic acid functio-nalized carbon dot and graphene quantum dots have been used for selective sensing of glucose. 17,18 Although boronic acid is well-known to bind diol readily to act as a carbohydrate receptor, several boronic acid-based sensors failed to recognize D-glucosamine, other aminosugars, glycans, etc. due to their low selectivities. On the other hand, glucosamine, an aminosugar, has been used over the years as a dietary supplement for the treatment of osteoarthritis in spite of its indistinct pharmacokinetics and pharmacodynamics. 19-21 In addition to its chondroprotective action, glucosamine has been believed to exert anticancer action for more than five decades. It shows growth inhibitory activity in cancer cells via affecting proteasomal activity. 22 There are also numerous contradictory findings on the efficiency of D-glucosamine in treating rheumatoid arthritis and gastric ulcers. 23-26 The development of luminescent quantum dot-based D-glucosamine sensors with a high sensitivity and selectivity will provide novel approaches for early clinical diagnosis of most D-glucosamine related diseases. Thus, it is of both biological and biomedical significance to construct sensing devices for probing D-glucosamine at normal cellular concentrations (1-2 mM). To date, very few fluorescence sensors have been reported for D-glucosamine, including monoaza-18-crown-6 ether and boronic acid as the receptor units, 27 metal complexes, 28 graphene oxide,

The present report highlights the role of comprehensive structure property relationships (SPRs) in the discovery of a new and more effective molecular system for sensing purposes. From an extensive survey of different classes of amino substituted annulated furanones, it was realized that with some exceptions, these functionalized furanones could sense Cu 2+ ions in the semi-aqueous phase irrespective of the nature of substituents; furthermore the same scaffolds could also detect Al 3+ , if the aldehydic position is specifically filled by a 3-indoyl group. As a result, amino substituted annulated furanones with 3-indoyl groups could detect both metal ions, response time of which mainly depends on the overall molecular framework. After replacing different furanone frameworks, a dual metal ion sensor (for Cu 2+ and Al 3+) with short response time and high selectivity and association constant was identified. The proposed bifunctional sensor displayed a distinct but observable response (turn off colorimetric for Cu 2+ and turn on fluorescence for Al 3+) to both metal ions with potential applications in the area of real sample analysis and membrane sensing.

Abstract The interaction of enzymes with nanoparticles is important in the field of biotechnology and medicine. Due to the various uses of cadmium telluride nanoparticle in protein science, biotechnology and biophysical chemistry, drug delivery, and cellular imaging, study of this nanoparticle interaction with protein seems to be necessary. Therefore, the interaction between cadmium telluride semiconductor nanoparticle and bovine alkaline phosphatase, a clinical marker enzyme, were investigated by assaying kinetic parameters and fluorescence absorption, UV–vis absorption spectra, and circular dichroism spectroscopic techniques. Obtained results showed that cadmium telluride nanoparticle could quench the fluorescence signal of bovine alkaline phosphatase effectively with a static quenching mechanism. Moreover, the binding of cadmium telluride nanoparticle to the enzyme was spontaneous and van der Waals and hydrogen bonding forces played a key role in the complex stabilization. Circular dichroism spectra measurements indicated that cadmium telluride nanoparticle decreased α-helical content and increased the β-sheet structure of bovine alkaline phosphatase. These findings suggest that cadmium telluride nanoparticle changes the structure and activity of bovine alkaline phosphatase.

The purpose of the present work was to develop a method for the sensing of thioacetamide by using spectroscop-ic techniques. Thioacetamide is a carcinogen and it is important to detect its presence in foodstuffs. Semiconductor quantum dots are frequently employed as sensing probes since their absorption and fluorescence properties are highly sensitive to the interaction with substrates present in the solution. In the present work, the interaction between thioacetamide and ZnO quantum dots has been investigated by using UV-visible, fluorescence and in-frared spectroscopy. Besides, dynamic light scattering (DLS) has also been utilized for the interaction studies. UV-visible absorption studies indicated the bonding of the lone pair of sulphur atom of thioacetamide with the surface of the semiconductor. The fluorescence band of the ZnO quantum dots was found to be quenched in the presence of micromolar concentrations of thioacetamide. The quenching was found to follow the Stern-Volmer relationship. The Stern-Volmer constant was evaluated to be 1.20 × 10 5 M −1. Infrared spectroscopic measurements indicated the participation of the\ \NH 2 group and the sulphur atom of thioacetamide in bonding with the surface of the ZnO quantum dots. DLS measurements indicated that the surface charge of the semiconductor was shielded by the thioacetamide molecules.

A cost effective reversible dual channel chemosensor (BT-1) has been synthesized for detection of Zn 2+ ion based on a benzo[d]thiazole Schiff base. It exhibits high selective and sensitive optical changes in fluorescence intensity for zinc metal ions. Optical chemosensor (BT-1) exhibited fluorescence off-on effect with Zn 2+ without any significant interference of other metal ions. The LOD of the optical chemosensors was calculated 0.11 μM for Zn 2+ ion. Probe BT-1 is applicable to electroanalytical recognition of Zn 2+ metal ion with polyvinyl chloride membrane sensing response. Reported chemosensor was provided high sensing response in real environmental sample with quick response time.