A hybrid catalyst-triggered cascade reaction for cholesterol detection using a smartphone-based miniature fluorescent apparatus.

A new hybrid biological-chemical catalyst, magnetic nanoparticles functionalized with cholesterol oxidase (Fe3O4/APTES/ChOx), was developed for cholesterol detection. In the presence of cholesterol, the enzyme produced H2O2, which facilitated the generation of fluorescent molecules from the fluorogenic substrate with the assistance of Fe3O4 nanoparticles. A smartphone camera with a miniature fluorescent apparatus was used to assess fluorescence emission. Then, a smartphone application was employed to translate the fluorescence intensity to the red, green, and blue (RGB) domain. The developed approach achieved excellent selectivity and acceptable performances while supporting an onsite analysis approach. The practical operational range spanned from 5 to 100 nM, with a detection limit of 0.85 nM. Fe3O4/APTES/ChOx was applied for up to four replicates of reuse and demonstrated stability for at least 30 days. The applicability of the method was evaluated in milk samples, and the results were in accordance with the reference method.

A portable fluorescence detection device based on a smartphone employing carbon nanodots for Mn2+ sensing.

The measurement of fluorescence emission for quantitative analysis is typically based on a traditional spectrofluorometer, which limits an onsite detection approach. Thus, an alternative device should be developed for fulfilling this analysis outside of the laboratory. Therefore, a low-cost, portable, and low-energy consumption fluorescence reader-based smartphone device was developed. An ultraviolet light-emitting diodes (UV-LED) was used to construct the fluorescence device-based smartphone as a low-power excitation light source. The smartphone camera was used as a detector for detecting photons from the fluorescence emission process of the fluorescence probe and was connected to a digital image platform. Transparent acrylic with orange and yellow colors was employed as a filter for reducing the interference from light source intensity. The obtained digital image was converted to red, green and blue (RGB) intensity using a custom-designed smartphone application. N,S-doped carbon nanodots (N,S-CDs) were demonstrated to be a good fluorescence indicator for determining trace quantities of Mn2+ in cosmetics. The approach exhibited high selectivity and sensitivity, detecting and quantifying analytes at 1-5 µM concentrations. Furthermore, the method's detection limit of 0.5 µM reflects its capacity to detect trace amounts of a target analyte. Mn2+ in cosmetic products was successfully analyzed using this device with high accuracy comparable with the results from inductively coupled plasma-optical emission spectroscopy (ICP-OES).

Supramolecular Structure and Photo-Thermo-Electric Property of Hydrogen-Bonded Liquid Crystalline Polymer Containing Poly(4-vinylpridine) and Cyanostilbene Side Chains.

A series of side-chain liquid crystalline polymers P4VP(CN-DBE)x , where x is the molar ratio of cyanostilbene (CN-DBE) to poly(4-vinylpyridine) (P4VP) repeating unit, was synthesized based on the intermolecular hydrogen bonding between P4VP and CN-DBE. Their luminescent property, liquid crystalline structure and photo-thermo-electric property were elucidated using photoluminescence spectra, X-ray diffraction, thermal imaging and thermoelectric experiments. With the increase of x, the supramolecular system can be changed from lamellar structure to hexagonal columnar structure. Moreover, the P4VP(CN-DBE)x polymer with columnar structure exhibits more efficient photothermal effect. The temperature of P4VP(CN-DBE)0.6 can rise to 130 °C within 10 s under the irradiation of ultraviolet lamp. In addition, the supramolecular system possesses unique photo-thermo-electric conversion ability, and 25 mA current can be detected in the circuit coupled with the thermoelectric module. This work broadens the potential applications of hydrogen-bonded polymer, and provides a simple and facile strategy to prepare liquid crystalline polymers with photo-thermo-electric property.

Tetraphenylethylene sulfonate derivative as turn-on fluorescent sensor for berberine chloride detection in aqueous solution.

A negatively-charged tetraphenylethylene derivative (TPE-SE) was designed and synthesized as turn-on fluorescent sensor for berberine chloride (BBC) detection in aqueous solution. The fluorescent property and detection mechanism were elucidated by UV-vis absorption spectra, photoluminescence spectra, dynamic light scattering experiments. The results reveal that the BBC can lead to aggregation-induced emission of TPE-SE due to the electrostatic interactions, endowing TPE-SE with excellent turn-on detecting ability, high selectivity and sensitivity to BBC. The detection limit is as low as 6.58 × 10-6M. These results should be applicable to fabricate special turn-on fluorescent sensors towards various antibiotics, and it is crucially important for achieving reasonable control and intake of small biomolecules.

Smartphone-based portable fluorescence sensor with gold nanoparticle mediation for selective detection of nitrite ions.

A simple, portable device for the detection of NO2- via a fluorescence method was developed. The proposed device consisted of a dark box containing a blue LED as a low-power excitation light source and a smartphone with a mobile application for RGB analysis as a light detector. Detection was mediated by using synthesized cetyltrimethylammonium bromide-stabilized gold nanoparticles (CTAB-AuNPs). The CTAB-AuNPs were etched with NO2- to yield Au3+, which catalyzes the oxidation of o-phenylenediamine (OPD) in the presence of H2O2 to generate 2,3-diaminophenazine (DAP). Triton X-100 (TX-100) micelles were introduced to improve the DAP fluorescence emission. The fluorescence intensity of DAP was recorded by the smartphone in terms of RGB intensity, which was correlated with the NO2- concentration. This method provided a wide linear working concentration range (0.5-100 µM), a limit of detection of 0.17 µM and excellent selectivity for NO2- over other anions.

Simultaneous preconcentration and fluorescence detection of ATP by a hybrid nanocomposite of magnetic nanoparticles incorporated in mixed metal hydroxide.

A new approach for increasing the sensitivity of adenosine triphosphate (ATP) detection was demonstrated. The assay was based on the synergetic function of a hybrid nanocomposite (MNPs@MMH) composed of magnetic nanoparticles (MNPs) incorporated in a mixed metal hydroxide (MMH). MNPs@MMH can be utilized as an efficient green extractant and peroxidase catalyst. The trace level of ATP in the sample solution was first extracted by the MNPs@MMH hybrid nanocomposite through the ion exchange properties of MMH and adsorbed on the surface of the MNPs@MMH. The concentration of ATP was related to the fluorescence intensity of 2,3-diaminophenazine (DAP) generated from peroxidase-like activity of the MNPs in the presence of H2O2 and o-phenylenediamine (OPD). In the presence of ATP, the active surface of the MNPs was diminished, and the amount of DAP generated was reduced. Thus, the concentration of ATP was related to the degree of fluorescence decrease compared to the fluorescence intensity of the system without ATP. Based on the proposed strategy, a highly sensitive assay for ATP was achieved. This assay exhibited good selectivity for detection of ATP over derivatives and other common anions. The proposed assay allowed the detection of ATP in a concentration range of 2.5-20 µM with a detection limit of 0.41 µM.

Non-invasive wearable chemical sensors in real-life applications.

Over the past decade, non-invasive wearable chemical sensors have gained tremendous attention in the field of personal health monitoring and medical diagnosis. These sensors provide non-invasive, real-time, and continuous monitoring of targeted biomarkers with more simplicity than the conventional diagnostic approaches. This review primarily describes the substrate materials used for sensor fabrication, sample collection and handling, and analytical detection techniques that are utilized to detect biomarkers in different biofluids. Common substrates including paper, textile, and hydrogel for wearable sensor fabrication are discussed. Principles and applications of colorimetric and electrochemical detection in wearable chemical sensors are illustrated. Data transmission systems enabling wireless communication between the sensor and output devices are also discussed. Finally, examples of different designs of wearable chemical sensors including tattoos, garments, and accessories are shown. Successful development of non-invasive wearable chemical sensors will effectively help users to manage their personal health, predict the potential diseases, and eventually improve the overall quality of life.

A simple strategy to enhance the sensitivity of fluorescent sensor-based CdS quantum dots by using a surfactant for Hg2+ detection.

A simple strategy to enhance the detection sensitivity of fluorescent sensor-based CdS quantum dots (CdS QDs) for the detection of mercury ions (Hg2+) was demonstrated. L-Cysteine-capped CdS QDs (L-Cyst-CdS QDs) were synthesized and utilized as a probe for selective detection of Hg2+. The fluorescence intensity of the L-Cyst-CdS QDs was quenched in the presence of Hg2+. However, the detection sensitivity was unsatisfactory. Upon the addition of sodium dodecyl sulfate (SDS), the fluorescence intensity of L-Cyst-CdS QDs can be effectively enhanced. On the other hand, the fluorescence intensity of the L-Cyst-CdS QDs in the presence of SDS (SDS@L-Cyst-CdS QDs) was able to be dramatically decreased with the addition of Hg2+. Furthermore, the proposed sensor displayed excellent selectivity towards Hg2+ compared to other cations. Under optimized conditions, the proposed sensor could be applied to detect trace amounts of Hg2+ with a limit of detection of approximately 36 nM. The applicability of this sensor was demonstrated by the determination of Hg2+ in real water samples, and the results agreed with those obtained from cold vapor atomic absorption spectrometry (CVAAS).

A fluorescence AuNPs-LISA: A new approach for Opisthorchis viverrini (Ov) antigen detection with a simple fluorescent enhancement strategy by surfactant micelle in urine samples.

The colorimetric AuNPs-LISA is a new, powerful technique for the detection of Opisthorchis viverrini antigen (OvAg) in urine samples. However, the diagnostic sensitivity of the colorimetric AuNPs-LISA is powerless to screen ultralow concentrations of OvAg in urine samples in cases of early stage liver fluke infection. This work, we aimed to improve the diagnostic sensitivity of the colorimetric AuNPs-LISA by developing a new fluorescence AuNPs-LISA. O-phenylenediamine (OPD) was used as the chromogenic substrate instead of the tetramethylbenzidine (TMB) of the colorimetric AuNPs-LISA. Interestingly, the fluorescence of the OPD oxidation product by the peroxidase-like activity of labelled AuNPs can be extremely enhanced by a non-ionic surfactant, especially the Triton X-100. The proposed assay exhibited a dynamic linear detection of OvAg concentration in the range of 34.18 ng mL-1 to 273.44 ng mL-1 with the limit of detection at 36.97 ng mL-1 which the detection sensitivity enhancement around 1200-fold when comparing with the colorimetric AuNPs-LISA. This model exhibits high diagnosis sensitivity, specificity and accuracy, 91.28%, 91.75%, and 91.59%, respectively, compared to the traditional ELISA. The fluorescence AuNPs-LISA showed excellent potential for the diagnosis of OvAg in urine samples from endemic areas. This will provide an effective tool for the detection, control and elimination of human opisthorchiasis.

AuNPs-LISA, an efficient detection assay for Opisthorchis viverrini (Ov) antigen in urine.

The enzyme-linked immunosorbent assay (ELISA) is currently a powerful technique for the detection of Opisthorchis viverrini antigen (OvAg) in urine samples. However, its sensitivity and analysis time need to be improved. In the present study, we aimed to improve the signal enhancing system of traditional ELISA by using gold nanoparticles (AuNPs) with peroxidase-like activity on its surface instead of the horseradish peroxidase (HRP) system. The catalytic activity of the AuNPs probe can be boosted by the gold enhancing solution and the addition of ATP. The catalytic ability of the AuNPs probe depended on the probe and the H2O2 concentration. The proposed approach can reduce the number of the traditional ELISA steps with better detection sensitivity. Interestingly, the limit of detection (LOD) of the test was 23.4 ng mL-1, substantially lower than the 93.8 ng mL-1 for the traditional ELISA. The AuNPs-LISA assay showed higher sensitivity and specificity, 93.81% and 91.34%, respectively, compared to the traditional ELISA. The proposed assay was successfully applied for the detection of OvAg in urine samples. This will provide an effective tool for the detection, control and elimination of human opisthorchiasis.

Highly selective circular dichroism sensor based on d-penicillamine/cysteamine­cadmium sulfide quantum dots for copper (II) ion detection.

A highly selective circular dichroism sensor based on cysteamine-capped cadmium sulfide quantum dots (Cys-CdS QDs) was successfully developed for the determination of Cu2+. Basically, the Cys-CdS QDs are not active in circular dichroism spectroscopy. However, the circular dichroism probe (DPA@Cys-CdS QDs) can be simply generated in situ by mixing achiral Cys-CdS QDs with D-penicillamine. The detection principle was based on measuring the circular dichroism signal change upon the addition of Cu2+. The strong CD signal of the DPA@Cys-CdS QDs dramatically decreased in the presence of Cu2+, while other cations did not result in any spectral changes. In addition, the degree of the CD signal decrease was linearly proportional to the concentration of Cu2+ in the range of 0.50-2.25 µM (r2 = 0.9919) with a detection limit of 0.34 µM. Furthermore, the proposed sensor was applied to detect Cu2+ in drinking water samples with %recovery values of 102-114% and %RSD less than 6%.

Fluorescence chemodosimeter for dopamine based on the inner filter effect of the in situ generation of silver nanoparticles and fluorescent dye.

A new strategy for the sensitive and selective detection of dopamine (DA) was proposed. The chemodosimeter design was based on the measurement of the fluorescent quenching of fluorescein dye caused by the in situ generation of silver nanoparticles (AgNPs). The AgNPs can be simply generated by a reaction between DA and Ag+ in the presence of polymethacrylic acid (PMAA). In addition, the generated AgNPs possess the maximum surface plasmon resonance (SPR) at 440 nm and an increase in the SPR intensity with an increasing DA concentration. Basically, fluorescein dye can emit the fluorescent intensity maximum at 513 nm with excitation at 487 nm. Thus, fluorescent quenching was achieved due to an inner filter effect from the overlap between the excitation spectrum of the fluorescein dye and the SPR spectrum of the generated AgNPs. The degree of fluorescent quenching linearly depends on the number of generated AgNPs that can be directly related to the concentration of DA. The proposed chemodosimeter can be used to detect DA in a working linear concentration range of 1.0-5.0 µM at a detection limit of 10.6 nM. This chemodosimeter was successfully applied to determine DA in a real urine sample and a dopamine injection formulation with satisfactory results.

A new formaldehyde sensor from silver nanoclusters modified Tollens' reagent.

A selective colorimetric assay for detecting formaldehyde (FA) was proposed based on silver nanoclusters (AgNCs) templated by polymethacrylic acid (PMAA). The chemodosimeter was easily fabricated by the formation of Tollens' reagent in the presence of AgNCs (AgNCs@Tollens). The detection principle was based on the change in the color caused by the change in the particle size from nanoclusters (no LSPR) to nanoparticles (with LSPR) upon the reduction of Tollens' reagent by FA. In the presence of FA, the intensity of a new absorbance band with a maximum at a wavelength of 430 nm corresponding to the LSPR of the AgNPs linearly increased as a function of the FA concentration, exhibiting a color change that could be observed by the naked eye. This method provided a working range of 30-50 µM with lower detection limit (LOD) of 27.99 µM. The proposed method exhibited excellent selectivity towards FA over other aldehyde-containing compounds.

A fluorescent sensor based on thioglycolic acid capped cadmium sulfide quantum dots for the determination of dopamine.

A fluorescent sensor based on thioglycolic acid-capped cadmium sulfide quantum dots (TGA-CdS QDs) has been designed for the sensitive and selective detection of dopamine (DA). In the presence of dopamine (DA), the addition of 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS) activates the reaction between the carboxylic group of the TGA and the amino group of dopamine to form an amide bond, quenching the fluorescence of the QDs. The fluorescence intensity of TGA-CdS QDs can be used to sense the presence of dopamine with a limit of detection of 0.68µM and a working linear range of 1.0-17.5µM. This sensor system shows great potential application for dopamine detection in dopamine drug samples and for future easy-to-make analytical devices.

Cysteamine-capped copper nanoclusters as a highly selective turn-on fluorescent assay for the detection of aluminum ions.

A new type of copper nanoclusters was synthesized by a one-pot reaction using cysteamine as a capping agent and reducing agent (Cys-CuNCs). The synthesized CuNCs exhibited a spherical shape and a monodisperse and strong fluorescent emission characteristic peak at 430nm when exciting at 330nm. The Cys-CuNCs were demonstrated as a fluorescent chemodosimeter for the selective detection of Al3+. In the presence of Al3+, the fluorescent emission of the Cys-CuNCs was considerably enhanced, while other studied metal ions did not show this phenomenon. The fluorescent intensity near 380nm linearly increased with an increasing Al3+ concentration. The proposed method provided a working range of 1-7µM with a low detection limit of 26.7nM and was applied to determine Al3+ in drinking water samples with satisfactory results.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots.

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd2+ and S2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd2+, S2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd2+ or S2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd2+ and S2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200µM and 7-125µM with detection limits of 59.7 and 1.6µM for Cd2+ and S2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd2+) and HPLC (for S2-).

Cysteamine capped CdS quantum dots as a fluorescence sensor for the determination of copper ion exploiting fluorescence enhancement and long-wave spectral shifts.

We described a turn-on fluorescence sensor for the determination of Cu(2+) ions, utilizing the quantum confinement effect of cadmium sulfide quantum dots capped with cysteamine (Cys-CdS QDs). The fluorescence intensity of the Cys-CdS QDs was both enhanced and red shifted (from blue-green to yellow) in the presence of Cu(2+). Fluorescence enhancement was linearly proportional to the concentration of Cu(2+) in the concentration range 2 to 10µM. Other cations at the same concentration level did not significantly change the intensity and spectral maxima of Cys-CdS QDs, except Ag(+). The limit of detection was 1.5µM. The sensor was applied to the determination of Cu(2+) in (spiked) real water samples and gave satisfactory results, with recoveries ranging from 96.7 to 108.2%, and with RSDs ranging from 0.3 to 2.6%.

Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine.

A new chemical sensor based on the measuring of circular dichroism signal (CD) was fabricated from cysteamine capped cadmium sulfide quantum dots (Cys-CdS QDs). The chiral-thiol molecules, d-penicillamine (DPA) and l-penicillamine (LPA), were used to evaluate potentials of this sensor. Basically, DPA and LPA provide very low CD signals. However, the CD signals of DPA and LPA can be enhanced in the presence of Cys-CdS QDs. The CD spectra of DPA and LPA exhibited a mirror image profile. Parameters affecting the determination of DPA and LPA were thoroughly investigated in details. Under the optimized condition, the CD signals of DPA and LPA displayed a linear relationship with the concentrations of both enantiomers, ranging from 1 to 35 µM. Detection limits of this sensor were 0.49 and 0.74 µM for DPA and LPA, respectively. To demonstrate a potential application of this sensor, the proposed sensor was used to determine DPA and LPA in real urine samples. It was confirmed that the proposed detection technique was reliable and could be utilized in a broad range of applications.

A circular dichroism sensor for Ni(2+) and Co(2+) based on L-cysteine capped cadmium sulfide quantum dots.

A new circular dichroism sensor for detecting Ni(2+) and Co(2+) was proposed for the first time using chiral chelating quantum dots. The detection principle was based on changing of circular dichroism signals of the chiral quantum dots when forming a chiral complex with Ni(2+) or Co(2+). L-Cysteine capped cadmium sulfide quantum dots (L-Cyst-CdS QDs) were proposed as a chiral probe. The CD spectrum of L-Cyst-CdS QDs was significantly changed in the presence of Ni(2+) and Co(2+). On the other hand, other studied cations did not alter the original CD spectrum. Moreover, when increasing the concentration of Ni(2+) or Co(2+), the intensity of the CD spectrum linearly increased as a function of concentration and could be useful for the quantitative analysis. The proposed CD sensor showed linear working concentration ranges of 10-60 µM and 4-80 µM with low detection limits of 7.33 µÐœ and 1.13 µM for the detection of Ni(2+) and Co(2+), respectively. Parameters possibly affected the detection sensitivity such as solution pH and incubation time were studied and optimized. The proposed sensor was applied to detect Ni(2+) and Co(2+) in real water samples, and the results agreed well with the analysis using the standard ICP-OES.

Cysteamine CdS quantum dots decorated with Fe3+ as a fluorescence sensor for the detection of PPi.

A new sensitive and selective fluorescence sensor for the detection of pyrophosphate (PPi) in aqueous media based on the Fe(3+) decorated cysteamine CdS QDs ([Cys-CdS QDs]-Fe(3+)) was proposed. The presence of PPi can induce the fluorescence quenching of [Cys-CdS QDs]-Fe(3+) due to the high formation constants between the phosphate group and Fe(3+). Because the complex between Fe(3+) and PPi acts as an efficient quencher, the concentration of PPi can be evaluated by tracking the degree of fluorescence quenching. The fabricated sensor was optimized to obtain the best sensor selectivity and sensitivity. Under optimal conditions, a linear relationship between the fluorescence response and the concentration of PPi was established in the range of 0.5-10 µM. The limits of detection and quantitation for PPi were found to be 0.11 and 2.78 µM, respectively. Furthermore, the proposed sensor exhibited high selectivity toward PPi relative to other common anions. The proposed sensor was successfully applied to the detection of PPi in urine samples with satisfactory results.