Sensor In Aqueous Solution Research Articles

Label-free detection of Acinetobacter baumannii through the induced fluorescence quenching of thiolated AuAg nanoclusters

The development of time-saving analytical methods for detection of Acinetobacter baumannii is of paramount importance. In this work, we have developed a two-step strategy to prepare highly photoluminescent AuAg nanoclusters (NCs) by using Ag+ as linkers to connect the Au+-thiol motifs forming Au+/Ag+-thiol motifs on the tailored thiolated Au NCs, resulting in a significant photoluminescence enhancement. The strong photoluminescence of the as-synthesized AuAg bimetallic NCs can be rapidly and selectively quenched by A. baumannii due to its induced agglomeration of AuAg bimetallic NCs, which allows this fluorescent material to act as a label-free A. baumannii sensor in aqueous solution. A linear relationship was demonstrated between the fluorescence intensity of the thiolated AuAg bimetallic NCs and the concentration of A. baumannii, in the range of 1 × 104 − 5 × 107 colony forming unit (CFU) /mL with a limit of detection of 2.3 × 103 CFU/mL. The A. baumannii content in sputum was also analyzed. As far as we know, this is the first report of a fluorescent sensor for the detection of A. baumannii. This approach represents a rapidly alternative method for the analysis of sputum A. baumannii in clinical diagnosis.

Solvent-Triggered Reversible Phase Changes in Two Manganese-Based Metal-Organic Frameworks and Associated Sensing Events.

A flexible Mn-based MOF, Mn-sdc-1, has been successfully synthesized by using the ligand 4,4'-stilbenedicarboxylic acid (H2 sdc). Attributed to the flexibility of the framework, Mn-sdc-1 can transform into a new phase (Mn-sdc-2) with completely different structural geometry; this is induced by trace levels of H2 O at room temperature. Reversibly, the transformation from Mn-sdc-2 to Mn-sdc-1 can be triggered by DMF upon heating beyond 100 °C. These results inspired a study of the influences of temperature and H2 O volume in the solid-state transformation of two MOF phases and, for the first time, a phase diagram of MOFs has been depicted. This phase diagram reflects the gradual H2 O-/temperature-dependent changes between Mn-sdc-1 and Mn-sdc-2, which is very meaningful in achieving the controllable synthesis of these two MOFs and lead to targeting the desired water-stable structure. As a result, the obtained water-stable Mn-sdc-2 can be developed as an excellent Pb2+ sensor in aqueous solution through the luminescence quenching effect with a limit of detection of 31.4 nm.

Biodegradable Microparticles for Simultaneous Detection of Counterfeit and Deteriorated Edible Products.

In an era of globalized trade relations where food and pharmaceutical products cross borders effortlessly, consumers face counterfeit and deteriorated products at elevated rates. This paper presents multifunctional, biodegradable hydrogel microparticles that can provide information on the authenticity and the potential deterioration of the tagged food or pharmaceutical formulations. These microparticles integrate spatially patterned authenticity code with two sensors-the first one detects possible presence of pathogenic microbes through monitoring pH while the second one identifies products stored above optimal temperatures via optical monitoring of the microparticle degradation. Particles are synthesized from a biocompatible polymer and a photoinitiator, dextran modified with 2-hydroxyethylmethacrylate and riboflavin, respectively, using a continuous, high throughput method stop-flow lithography. The proposed synthesis approach also enables crosslinking with visible light bringing about additional flexibility to flow lithography. Model liquid and solid food and pharmaceutical products are successfully labeled with microparticles and the functionality of the sensors in aqueous solutions is demonstrated.

Temperature Self-Compensated Optical Waveguide Biosensor Based on Cascade of Ring Resonator and Arrayed Waveguide Grating Spectrometer

A temperature self-compensated optical waveguide biosensor employing the cascade of a ring resonator and an arrayed waveguide grating (AWG) spectrometer based on silicon-on-insulator platform is proposed and theoretically investigated. By means of appropriately choosing the waveguide widths for ring waveguide and array waveguide, respectively, the AWG spectrometer is designed to have the same temperature dependence as the ring sensor in aqueous solution, pertinent to most biosensing applications, with temperature change to eliminate the temperature-induced sensor signal change in detection result. A center of gravity detection technique is used for processing the power distributions at all output channels of the AWG spectrometer to derive the resonance wavelength of the ring sensor. The simulated results show that the resonance wavelength shifts derived from the AWG spectrometer for the ring sensor/sensor arrays are only dependent on the refractive index change of the aqueous solution and remain unchanged regardless of the environmental temperature variation. Compared with the conventional measurement for the ring sensor, this proposed optical waveguide biosensor without the needs for an external high-resolution light source/spectrometer and extra processing for the detected data to eliminate the temperature influence can find an application in smartphones/potable sensor detection systems for on-site testing.

Rapid and sensitive detection of hemoglobin with gold nanoparticles based fluorescence sensor in aqueous solution

A novel gold nanoparticles (AuNPs)-based fluorescence assay had been developed for the detection of hemoglobin (Hb). The method relied on the high selectivity of surface imprinting technique and the strong fluorescence property of AuNPs. Herein, firstly, the carboxyl modified AuNPs were initially anchored on the amino-functionalized silica nanoparticles under the assistance of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) and 1-hydroxy-5-pyrrolidinedione (NHS). Then, the Hb-imprinted polymer layer was wrapped on the surface of SiO2/AuNPs via a sol–gel surface imprinting technique. The generated SiO2/Au/MIPs as fluorescence sensor owned both sensitive detection of AuNPs and specific selectivity of molecularly imprinted polymer. The conditions such as pH, stability and effect of the fluorescence sensor concentration were investigated to search the optimized detection conditions. For the optimized conditions, the fluorescence-quenching detection presented a satisfactory linearity with Hb concentrations in the range of 0.1–20 μmol L−1 and the detection limit was 0.03 μmol L−1. Moreover, through the investigation of selective and competitive quenching, the fluorescence sensor exhibited satisfying selectivity and high binding affinity to Hb under the existence of its possibly competing molecules, such as bovine serum albumin (BSA), bovine hemoglobin (BHb), albumin, chicken egg (ACE). The results proved that the fluorescence sensor was succeeded to be used in the field of rapid recognition and determination of Hb even though existing of other complex proteins.

Optical waveguide modeling of refractive index mediated pH responses in silica nanocomposite thin film based fiber optic sensors

Recent experiments have demonstrated a pH-dependent optical transmission of silica based nanocomposite thin film enabled evanescent wave absorption spectroscopy based fiber optic sensors in aqueous solutions. Although the response was observed to linearly correlate with the pH-dependent surface charge density of the silica matrix, the responsible mechanism was not fully clarified. In this manuscript, an optical waveguide model is applied to describe observed responses through a modified effective refractive index of the silica matrix layer as a function of the solution phase pH. The refractive index dependence results from a surface charge dependent ionic adsorption, resulting in concentration of ionic species at charged surfaces. The resultant effective index modification to porous silica is estimated through effective medium theories and applied to an optical waveguide model of a multi-mode fiber optic based sensor response capable of reproducing all experimental observations reported to date.

Acridine-based complex as amino acid anion fluorescent sensor in aqueous solution

Novel acridine-based fluorescence sensors containing alaninol ligands, L1 and D1, were designed and synthesized. The structure of the compound was characterized by IR, 1H NMR, 13C NMR, MS spectra. L1 and D1 possess efficient Cu2+ cation ON–OFF selective signaling behavior based on ligand-to-metal binding mechanism at physiological pH condition. Additionally, the L1–Cu(II) and D1–Cu(II) complexes could further serve as reversible OFF–ON signaling sensing ensemble to allow ratiometric response to amino acid anion in aqueous solution.

Rational design, synthesis of reaction-based dual-channel cyanide sensor in aqueous solution

A new dual-channel sensor for the detection of cyanide was developed based on the conjugated of naphthalene and malononitrile. Upon the addition of CN−, the sensor displayed very large blue-shift in both fluorescence (80nm) and absorption (120nm) spectra. The sensor of cyanide was performed via the nucleophilic attack of cyanide anion to vinylic groups of the sensor with a 1:1 binding stoichiometry and the color changed of the sensor is mainly due to the intramolecular charge transfer process improvement. The intramolecular charge transfer progress was blocked with color changed and fluorescence blue-shift. The mechanism of sensor reaction with CN− ion was studied using 1H NMR and mass spectrometry.

Design, synthesis and photophysical properties of 8-hydroxyquinoline-functionalized tripodal molecular switch as a highly selective sequential pH sensor in aqueous solution

TAME5OX can act as a good candidate with potential applications in chemical and biological fields. Fluorescence reduction due to ESIPT between protonated NH+ ∼ –OH and deprotonated N ∼ –O− forms was proven by DFT calculation.

A novel Schiff-base as a Cu(II) ion fluorescent sensor in aqueous solution

A new fluorescent Cu(II) sensor (L) obtained from the Schiff base of 5,5′-methylene-bis-salicylaldehyde with amidol (2,4-diaminophenol) was synthesized and characterized by FT-IR, MS, 1H NMR, 13C NMR techniques. In the presence of pH 6.5 (KHPO4–Na2HPO4) buffer solutions, copper reacted with L to form a stable 2:1 complex. Fluorescence spectroscopic study showed that Schiff base is highly sensitive towards Cu(II) over other metal ions (K+, Na+, Al3+, Ni2+, Co2+, Fe3+, Zn2+, Pb2+) in DMSO/H2O (30%, v/v). The sensor L was successfully applied to the determination of copper in standard reference material. The structural properties and molecular orbitals of the complex formed between L and Cu2+ ions were also investigated using quantum chemical computations.

A Schiff base derivative from cinnamaldehyde for colorimetric detection of Ni2+ in water

A novel Schiff base (L1) derivative from cinnamaldehyde with a simple structure was synthesized and evaluated as a sensitive colorimetric Ni2+ sensor in aqueous solution. Addition of nickel dissolved in water into a L1 solution produced a rapid color change from faded yellow to deep orange, corresponding to a large red shift in the absorption peak from 435 to 480nm. L1 exhibited a detection limit for Ni2+ in water of 1×10−7M measured by absorption spectroscopy, whereas by naked eye the detection limit was of the order of 5×10−6M. Interaction between L1 and other biologically and environmentally relevant metal ions such as Hg2+, Pb2+, Co2+, Cu2+ and Mn2+, induced minimal spectral changes. These results show that the Schiff base L1 could be an excellent Ni2+ chemosensor with high metal selectivity and with the capability to perform the detection in water over a pH range of 5.5–8.

Visual sensing of Hg2+ using unmodified Au@Ag core–shell nanoparticles

In this work, we have developed a novel visual Hg2+ sensor in aqueous solution using unmodified Au@Ag core–shell nanoparticles at room temperature, based on a redox reaction between Ag-shell and Hg2+. The prepared Au@Ag core–shell nanoparticles exhibited good monodispersity. In the presence of Hg2+, Hg2+ was reduced into Hg (0) by Ag-shell, and deposited on the surface of Au-core to form Au–Hg alloys and caused nanoparticles aggregation, leading to the color changes of the solution from yellow to purplish red, and the surface plasmon resonance spectra of Au@Ag core–shell nanoparticles red shift. Under the optimal conditions, the visual sensor could selectively detect Hg2+ as low as 0.4 µM with the naked eye and 5.0 nM by UV–vis spectra analysis methods. The designed sensor had several advantages: (1) the nanoparticles surface need not be functionalized. (2) The color change of the solution was in 2 s and could easily be observed with naked eyes. The visual sensor had been applied to detection of Hg2+ in tap and lake water, which obtained satisfied result.

Dithiothreitol-capped fluorescent gold nanoclusters: An efficient probe for detection of copper(II) ions in aqueous solution

We report here a Green method for the synthesis of fluorescent gold nanoclusters using dithiothreitol (DTT) as both a capping agent and reducing agent at 22°C and pH 8. The physical and chemical properties of the synthesized AuNCs@DTT were studied by TEM and UV–vis absorption, fluorescence, and X-ray photoelectron spectroscopy. AuNCs@DTT recognizes cupric ions with high selectivity and sensitivity, which allows this material to act as a copper(II) sensor in aqueous solution. A linear relationship was observed between the fluorescence intensity of the DTT capped gold nanoclusters and the concentration of copper(II) ions, in the range of 0–60μM with a detection limit of 80nM. The copper content in serum was also analyzed by using this copper sensor. It was shown that data obtained using the proposed method was comparable to values obtained by the traditional colorimetric method. This technique represents an alternative method for the determination of serum copper in clinical diagnosis especially for those laboratories which lack expensive analytical facilities.

Polypyrrole Composite Film for Highly Sensitive and Selective Electrochemical Determination Sensors

In this paper, polypyrrole (PPy) and benz[a]anthracene-7,12-dione (BaD) were electro-polymerized onto a pyrolytic graphite electrode (PGE), constructing a novel BaD/PPy/PGE platform for electrochemical sensoring. The morphology and electrochemical properties of the fabricated BaD/PPy/PGE were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. Furthermore, the electrochemical behavior of benzo[k]fluoranthene (BkF) at the BaD/PPy/PGE was investigated. Due to the specific interactions between BkF and BaD, a wide linear range of BkF detection from 1.0×10−12 to 1.0×10−9M with good linearity (R2=0.9962) and a low detection limit (1.0×10−13M, S/N=3) were demonstrated. Importantly, other similar aromatics which had one ring or more than two rings, such as benzo[a]anthracene, benzo[a]pyrene, pyrene, benzo[ghi]peryle, anthracene, phenanthrene, naphthalene and parachlorophenol, showed insignificant interference on BkF detection. Consequently, this novel BaD/PPy/PGE with excellent stability and selectivity holds promise as an effective BkF electrochemical sensor in aqueous solution. As an example for its practical application, the newly developed sensor was applied to quantitative determination of BkF in waste water samples obtained from a coking plant with satisfactory sensitivity, selectivity, and reversibility.

Turn-off Fluorescence Chemosensor for Iron with Bis(2-aminoethyl)-2-(9-fluorenyl)malonamide Functionlized SBA-15

An bis(2-aminoethyl)-2-(9-fluorenyl)malonamide as fluorophore ligand was immobilized onto mesoporous silica type SBA-15 via post synthesis grafting. The obtained material was characterized by small and wide angle X-ray diffraction, N2 adsorption-desorption, Fourier transform infrared spectroscopy, Raman spectroscopy and thermogravimetric analysis that indicate the successful immobilization of the ligand on the surface of mesoporous silica. The sensing ability of the obtained material was studied by addition of the cations Fe(3+), Mg(2+), Cr(3+), Co(2+), Ni(2+), Cu(2+), Hg(2+) and Zn(2+) to water suspensions of the assayed solid. Of all the cations tested addition of Fe(3+) ion to a suspension of this material resulted in the largest decrease in the fluorescence intensity. Turn-off photoluminescence of this material was remarkably observed for iron ions in comparing of the other cations. A good linearity between the fluorescence intensity of this material and the concentration of Fe(3+) ion is constructed, which enables it as a fluorescence chemosensor for detecting the Fe(3+) ion with a suitable detection limit of 1.35 × 10(-5). It can be introduced as a novel fluorescent sensor in aqueous solution for a lot of practical applications in chemical, environmental and biological systems.

Ultra high sensitivity chemical photonic sensing by Mach–Zehnder interferometer enhanced Vernier-effect

In this paper an ultra high sensitivity chemical photonic sensor is proposed, employing a Mach–Zehnder interferometer (MZI)-enhanced Vernier effect. The proposed sensor is demonstrated to reach ultra high overall sensitivity (>1000 μm/RIU) and very low limit of detection (LOD < 10−6 RIU), with a compact, standard SOI chip. Furthermore, two very efficient sensors are designed. The first one is a CO2 sensor for health safety purpose, able to detect gas concentration as low as 5000 ppm. The second one is an ammonia sensor in aqueous solution, able to detect ammonia concentrations down to 2 ppm. The designed sensors are proposed in silicon on insulator (SOI) technology due to its compatibility with standard CMOS technology, but the enhanced Vernier effect could be applied to each technology allowing to simultaneously fabricate ring resonators and MZIs.

Solvent controlled sugar–rhodamine fluorescence sensor for Cu2+ detection

A "turn-on" fluorescence probe for Cu(2+) detection has been reported according to a Cu(2+) triggered spirolactam ring-opening reaction. The probe is a double-responsive fluorescent and colorimetric Cu(2+)-specific sensor in aqueous solution containing 20% of acetonitrile with high selectivity and excellent sensitivity (limit of detection is 12 μg L(-1)). Furthermore, the significant color changes visible to the naked eye at the concentration of 3 μM (ca. 0.20 mg L(-1)) are about ten times lower than the WHO (World Health Organization) recommended level (2.0 mg L(-1)) for Cu(2+) ions in drinking water.

Fluorescence enhancement of cationic diacetylene-contained polyelectrolyte by anions and cations and application for sensitive and selective detection of Hg2+

An unusual phenomenon, the fluorescence enhancement of cationic conjugated fluorene-co-carbazole-co-diacetylene polymers (CPFC) by both anionic and cationic ions, was reported. The fluorescence enhancement of CPFC strongly depended on the nature of the ions and the counterions. In the solution of DMF/H2O, PO, CO and Hg2+ showed the most pronounced fluorescence enhancement response of CPFC (more than 10-fold). The fluorescence of CPFC was quenched by K4[Fe(CN)6, and then could be recovered with the addition of Hg2+. Based on these observations, a simple and sensitive fluorescent “turn-on” sensor in aqueous solution for Hg2+ was developed by use of a system of CPFC/ K4[Fe(CN)6]. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011

Pulsed Method for Characterizing Aqueous Media Using Nanowire Field Effect Transistors

This paper presents a method for using nanowire field-effect transistors (NW-FETs) as sensors in aqueous solutions without the need for a reference electrode. A pulsed-gate potential method is used to reduce instabilities related to the dynamics of ions and other charged species present in the solution. Application of this method results in a significant increase in the stability of the electrical properties of the devices, enabling reproducible characterization of aqueous media with NW-FETs. We show that this method can be applied to perform pH measurements with a silicon NW-FET.

An effective Cu(ii) quenching fluorescence sensor in aqueous solution and 1D chain coordination polymer framework

In the article, a novel fluorescent probe for the copper cation based on fluorescence quenching mechanism was designed. It exhibited high selectivity for Cu(II) over other common metal ions in aqueous media. Furthermore the coordination between Cu(II) and the organic molecule sensor fabricated an interesting 1D chain coordination polymer framework.