A novel fluorescent sensor for selective rifampicin detection based on the bio-inspired molecularly imprinted polymer-AgInS2/ZnS quantum dots.

A fluorescent sensing material based on the ternary core-shell quantum dots with outstanding optical properties and a bio-inspired molecularly imprinted polymer (MIP) as a recognition element has been prepared for selective detection of rifampicin (RFP). Firstly, AgInS2/ZnS core/shell quantum dots (ZAIS QDs) were prepared by a hydrothermal process. Then, the fluorescent sensor was prepared by coating these QDs by a dopamine-based MIP layer. The fluorescence of MIP@ZAIS QDs was quenched by RFP probably due to the photoinduced electron transfer process. The quenching constant was much higher for MIP@ZAIS QDs than the non-imprinted polymer@QDs, indicating that MIP@ZAIS QDs could selectively recognize RFP. Under the optimized conditions, the sensor had a good linear relationship at the RFP concentration range of 5.0 to 300 nM and the limit of detection was 1.25 nM. The respond time of the MIP@ZAIS QDs was 5 min, and the imprinting factor was 6.3. It also showed good recoveries ranging from 98 to 101%, for analysis of human plasma samples. The method is simple and effective for the detection of RFP and offers a practical application for the rapid analysis of human plasma samples.

A smartphone-assisted fluorescent sensing platform for ochratoxin A using Mn-doped CsPbBr3 perovskite quantum dots embedded in the mesoporous silica as a ratiometric probe.

Food sources are susceptible to contamination with ochratoxin A (OTA), which is a serious threat to human health. Thus, the construction of novel, simple sensing platforms for OTA monitoring is of utmost need. Manganese-doped lead halide perovskite quantum dots encapsulated with mesoporous SiO2 (Mn-CsPbBr3 QDs@SiO2) were prepared here and used as a ratiometric fluorescent probe for OTA. Mn-CsPbBr3 QDs, synthesized at room temperature, exhibit dual emission with maximum wavelengths of 440 and 570 nm and, when embedded in the SiO2 layer, produce a stable and robust photoluminescence signal. By adding OTA to the probe, emission at 440 nm increases while emission at 570 nm decreases, so a ratiometric response is obtained. Experimental variables affecting the probe signal were studied and optimized and the mechanism of sensing was discussed. This ratiometric sensor demonstrated excellent selectivity and low detection limit (4.1 ng/ml) as well as a wide linear range from 5.0 to 250 ng/ml for OTA. A simple portable smartphone-based device was also constructed and applied for the fluorescence assay. With different OTA concentrations, the multicolor transition from pink to blue under a UV lamp led to simple visual and smartphone-assisted sensing of OTA by using a color analyzing application. Satisfactory recoveries in black tea, coffee, moldy fig and flour samples confirmed the reliability of the assay. The accuracy of the probe was proved by comparison of the results with high-performance liquid chromatography (HPLC).

A fluorescent magnetic nanosensor for imidacloprid based on the incorporation of polymer dots and Fe3 O4 nanoparticles into the covalent organic framework.

A magnetic nanoprobe was designed for imidacloprid by encapsulating nonconjugated polymer dots (NCPDs) and Fe3 O4 nanoparticles in the covalent organic framework (COF). The fluorescence intensity of the COF-based nanocomposite is markedly suppressed by imidacloprid. As the absorption spectrum of imidacloprid was close to the band-gap of the NCPDs, and due to the presence of a nitro group (as an electron acceptor), the electrons can be easily transferred from the conduction band of NCPDs to the LUMO of imidacloprid, so fluorescence quenching was more likely to have been caused by the electron transfer process. The COF-based nanosensor was used for the determination of imidacloprid in the linear range 1.3-130 nM with a detection limit of 1.2 nM. The high sensitivity of the nanoprobe for imidacloprid is due to the combination of COF benefits (accumulation of the imidacloprid into the COF cavities) and the high adsorption ability of the Fe3 O4 nanoparticles, which leads to further enrichment of imidacloprid. The magnetic nature of the nanocomposite enables the preconcentration and easy separation of the analyte, and so reduces matrix interference and lowers the detection limits. The practicality of this nanoprobe was confirmed by quantification of imidacloprid in the wastewater and fruit juice samples.

Highly sensitive colorimetric assay for penconazole using gold nanostar-graphene quantum dot composite.

In this study, a simple and sensitive colorimetric method for penconazole sensing is reported. It is based on the etching/anti-etching strategy in which gold nanostar@graphene quantum dot (AuNS@GQD) nanocomposite acts as a sensing nanoprobe and IO4- as an etching agent. With adding IO4- to the solution of AuNSs@GQDs, the sharp tips of NSs are etched and they are transformed into nearly spherical nanostructures, and the color of the solution changes from green to violet. These changes can be attributed to the oxidation of gold atoms at the sharp corners and tips of NSs with I2, produced by the reaction of IO4- with AuNS@GQD solution. When penconazole is added into the system, the color and shape variations of AuNSs caused by periodate are impressively prevented. It can be assigned to the strong binding affinity between nitrogen atoms of penconazole and gold atoms, which protects them from etching by I2. This mechanism has been affirmed via transmission electron microscopy (TEM) and UV-Vis spectra. This approach exhibited a good linear relationship (R2 = 0.999) between the wavelength shift and penconazole concentration in the range of 5.0-1000.0 nM with a limit of detection (LOD) of 1.5 nM. The sensor is stable and reproducible and was used to measure penconazole in spiked water samples with recoveries over 97%.

Perovskite quantum dots as a chemiluminescence platform for highly sensitive assay of cefazolin.

This paper reports on a chemiluminescence (CL) probe consist of CsPbBr3 quantum dots (QDs) in organic phase together with Fe(II) and K2S2O8 in aqueous medium for the highly selective and sensitive determination of the antibiotic, cefazolin (CFZ). The CsPbBr3perovskite QDs prepared by the ligand assisted reprecipitation method, exhibit a narrow fluorescence at 533 nm under 460 nm excitation with a high quantum yield (42 %). The Fe(II) - S2O82- as an ultra-weak CL system is converted to a rather strong CL sensing platform in the presence of organic-phase CsPbBr3 QDs. It was observed that CFZ exerts an enhancement effect on the CL signal of the designed probe in the linear range of 25 - 300 nM, with a low limit of detection (9.6 nM). The introduced sensor has broad application prospects in biosensing, food detection, and other fields with recovery ranging from 94 to 106 %.

Sonochemically synthesized mesoporous cobalt oxide nanoparticles for luminol-enhanced chemiluminescence sensing.

In recent years, mesoporous cobalt oxides have attracted more attention due to their exceptional physical and chemical properties and their important applications in various fields. The synthesis of cobalt oxides of various sizes, morphologies, and porosity is still a challenging process. In this report, mesoporous Co3O4NPs with different porosity were synthesized through facile, one-step, and cost-effective routes, without using any complicated materials or instruments, via the sonochemical process. X-ray powder diffraction (XRD), BET, and transmission electron microscopy (TEM) were used to characterize the as-synthesized NPs. XRD technique was used to determine the crystal structure and phase of the NPs, BET to describe the porous nature of the NPs, and TEM to investigate the structure and morphology of the NPs. Next, the effect of as-synthesized Co3O4NPs as a catalyst for the luminol-H2O2chemiluminescence system was studied. Co3O4NPs were chosen since they have nanoscale size, high specific surface area, and mesoporous nature. Therefore, these NPs can form more active sites and thus show unique catalytic activity than common ionic catalysts such as Co2+, Fe3+, Cu2+used in the luminol-H2O2CL system. Finally, this system was used to detect and measure H2O2and glucose under optimal conditions. A good linear relationship was observed between the chemiluminescence intensity of the designed system and the concentration of H2O2and glucose. A linear range like 0.25-10 pM for H2O2and 1-30 nM for glucose was obtained. The excellent LOD of the proposed method for measuring H2O2was about 0.07 pM, and for measuring glucose was about 0.14 nM.

Eco-friendly nonconjugated polymer dots for chemiluminometric determination of 4-nitrophenol.

Polymer dots (PDs) are a new family of quantum dots for which their behavior and potential applications have not yet been completely explored. In this study, nonconjugated PDs were synthesized using a simple pyrolysis method and used for the chemiluminescence (CL) assay of 4-nitrophenol (4-NP). PDs increased the CL signal of the Ce(IV)-Na2 SO3 reaction 39-fold. Using the CL spectrum, it was concluded that the emission at 434 nm was generated by excited PDs (PDs*), which are produced by energy transfer from SO2 * to PDs. Our experiments showed that 4-NP enhanced the CL signal of the Ce(IV)-Na2 SO3 -PDs reaction. The mechanism of this effect was explored by obtaining CL, ultraviolet-visible, and Fourier transform infrared spectra. Due to the high sensitivity and selectivity of the CL system for 4-NP, a probe was designed to determine 4-NP in the linear range 1.0-500 nmol/L with a detection limit of 0.33 nmol/L. Different spiked real samples were successfully analyzed using this probe.

Plasmon-enhanced fluorimetric and colorimetric dual sensor based on fluorescein/Ag nanoprisms for sensitive determination of mancozeb.

A plasmon-enhanced fluorimetric and colorimetric dual sensor was designed to detect mancozeb based on fluorescein (as a fluorimetric reporter) and AgNPRs (as a fluorescence enhancer and colorimetric reporter). The sensing mechanism was based on the shape transformation of AgNPRs due to etching and anti-etching effect of S2O32- and mancozeb. We observed that AgNPRs enhanced the fluorescence intensity of fluorescein around 4-fold. By adding S2O32-, the AgNPR florescence enhancement effect decreased, also SPR peak of AgNPRs blue-shifted and the solution color altered from blue to purple. The fluorescein fluorescence intensity and AgNPR's SPR peak position restored in the presence of mancozeb due to its protecting effect on AgNPRs. The restored fluorescence intensity and the SPR wavelength shift were proportional to the mancozeb concentration at the range of 0.005-0.1 and 0.005-0.075 mg/L, respectively. The developed sensor was successfully applied to measure mancozeb in fruit juice samples.

A sensitive homogeneous enzyme assay for euchromatic histone-lysine-N-methyltransferase 2 (G9a) based on terbium-to-quantum dot time-resolved FRET.

Introduction: Histone modifying enzymes include several classes of enzymes that are responsible for various post-translational modifications of histones such as methylation and acetylation. They are important epigenetic factors, which may involve several diseases and so their assay, as well as screening of their inhibitors, are of great importance. Herein, a bioassay based on terbium-to-quantum dot (Tb-to-QD) time-resolved Förster resonance energy transfer (TR-FRET) was developed for monitoring the activity of G9a, the euchromatic histone-lysine N-methyltransferase 2. Overexpression of G9a has been reported in some cancers such as ovarian carcinoma, lung cancer, multiple myeloma and brain cancer. Thus, inhibition of this enzyme is important for therapeutic purposes. Methods: In this assay, a biotinylated peptide was used as a G9a substrate in conjugation with streptavidin-coated ZnS/CdSe QD as FRET acceptor, and an anti-mark antibody labeled with Tb as a donor. Time-resolved fluorescence was used for measuring FRET ratios. Results: We examined three QDs, with emission wavelengths of 605, 655 and 705 nm, as FRET acceptors and investigated FRET efficiency between the Tb complex and each of them. Since the maximum FRET efficiency was obtained for Tb to QD705 (more than 50%), this pair was exploited for designing the enzyme assay. We showed that the method has excellent sensitivity and selectivity for the determination of G9a at concentrations as low as 20 pM. Furthermore, the designed assay was applied for screening of an enzyme inhibitor, S-(5'-Adenosyl)-L-homocysteine (SAH). Conclusion: It was shown that Tb-to-QD FRET is an outstanding platform for developing a homogenous assay for the G9a enzyme and its inhibitors. The obtained results confirmed that this assay was quite sensitive and could be used in the field of inhibitor screening.

A Fatigue Damage Model for Life Prediction of Injection-Molded Short Glass Fiber-Reinforced Thermoplastic Composites.

Short glass fiber-reinforced (SGFR) thermoplastics are used in many industries manufactured by injection molding which is the most common technique for polymeric parts production. Glass fibers are commonly used as the reinforced material with thermoplastics and injection molding. In this paper, a critical plane-based fatigue damage model is proposed for tension-tension or tension-compression fatigue life prediction of SGFR thermoplastics considering fiber orientation and mean stress effects. Temperature and frequency effects were also included by applying the proposed damage model into a general fatigue model. Model predictions are presented and discussed by comparing with the experimental data from the literature.

A chemiluminescence probe enhanced by cobalt and nitrogen-doped carbon dots for the determination of a nitrosative stress biomarker.

A chemiluminometric method is introduced for the determination of the stress biomarker, 3-nitrotyrosine (3-NT) based on the H2O2-NaIO4 reaction enhanced by cobalt and nitrogen-doped carbon dots (Co,N-CDs). In this chemiluminescence (CL) system, the emission proved to be originated from the excited-state Co,N-CDs (λmax = 504 nm). Comparing the effect of Co,N-CDs with that of some other metal ion-doped CDs and undoped CDs indicated the high efficiency of Co,N-CDs in the CL amplification (about 1980-fold). This was attributed to the fact that Co,N-CDs, in addition to other functions, could act as catalytic center, to accelerate the decomposition of H2O2 and to increase the number of hydroxyl radicals. It was found that 3-NT inhibits the action of Co,N-CDs by an electron transfer process, leading to a decline in the CL intensity of the system. Therefore, a new CL sensing platform was introduced for the assay of 3-NT in the range 5.0 to 300 nM with a detection limit of 1.5 nM. The probe was utilized for the analysis of biological samples.

A new enhanced chemiluminescence reaction based on polymer dots for the determination of metronidazole.

Polymer dots (PDs) with non-conjugated functional groups are attracting nanomaterials due to their ease of synthesis, the biocompatibility of precursors, and low toxicity. In this work, PDs with non-conjugated groups were synthesized with a simple and straightforward method by Schiff base reaction. Then their possible application in the chemiluminescence (CL) reactions was explored. Results were shown that PDs increased the CL intensity of the NaIO4-fluorescein system about 15 times. Regarding the CL mechanism, we proved that the emitting species is fluorescein, which can be excited by the energy transfer from the excited-state PDs. It was observed that CL emission is promoted by the interaction of metronidazole (MND) with the PDs. Therefore, we designed a novel and sensitive assay for MND based on its enhancing effect on NaIO4-fluorescein-PDs CL system. The introduced assay showed a linear response in the range of 5.0-300 nM with a detection limit of 1.5 nM. The method was used for the determination of MND in spiked plasma samples.

Gold nanostar@graphene quantum dot as a new colorimetric sensing platform for detection of cysteine.

We here report on a facile method for preparation of gold nanostar-graphene quantum dot (AuNS@GQD) composite, which produces highly active surfactant-free AuNSs. The etching reaction of this composite with Na2SO3 was studied and used as a new sensing strategy for colorimetric detection of nM levels of cysteine. In the presence of Na2SO3, the shape of AuNSs changes to sphere-like nanoparticles, leading to a distinct color change of solution from light green to indigo. This phenomenon results from the redox reaction of Au atoms at the apexes and sharp corners of the NSs with oxygen which leads to the formation of [Au(SO3)2]3-. Our studies indicated that the stars with larger sizes show greater activity in etching reaction since they have more branches and sharper tips. Due to the strong coordination between Au and thiols, pre-added cysteine can protect the AuNSs from SO32- etching and so the shape and the color of AuNSs remain unaltered. This anti-etching effect was used for the detection of cysteine with the detection limit as low as 0.35 nM. The developed colorimetric sensor was validated by HPLC method and applied for analysis of human plasma samples.

Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications.

As a fascinating class of fluorescent carbon dots (CDs), doped-CDs are now sparked intense research interest, particularly in the diverse fields of biomedical applications due to their unique advantages, including low toxicity, physicochemical, photostability, excellent biocompatibility, and so on. In this review, we have summarized the most recent developments in the literature regarding the employment of doped-CDs for pharmaceutical and medical applications, which are published over approximately the past five years. Accordingly, we discuss the toxicity and optical properties of these nanomaterials. Beyond the presentation of successful examples of the application of these multifunctional nanoparticles in photothermal therapy, photodynamic therapy, and antibacterial activity, we further highlight their application in the cellular labeling, dual imaging, and in vitro and in vivo bioimaging by use of fluorescent-, photoacoustic-, magnetic-, and computed tomography (CT)-imaging. The potency of doped-CDs was also described in the biosensing of ions, small molecules, and drugs in biological samples or inside the cells. Finally, the advantages, disadvantages, and common limitations of doped-CD technologies are reviewed, along with the future prospects in biomedical research. Therefore, this review provides a concise insight into the current developments and challenges in the field of doped-CDs, especially for biological and biomedical researchers.

A Simple and Novel Sensor for the Determination of Acetamiprid Based on Its Reducing Effect on the Chemiluminescence of S, N-CQDs in CH3CN-H2O2 System.

A simple and novel method for the determination of acetamiprid in water samples is suggested. The method is based on the reducing effect of acetamiprid on the chemiluminescence intensity of new sulfur and nitrogen co-doped carbon dots (S, N-CQDs) in an acetonitrile-hydrogen peroxide (CH3CN-H2O2) system. The possible mechanism was investigated, and it was found that S, N-CQDs react with (1O2)2*, produced from the CH3CN-H2O2 reaction, leading to excited state S, N-CQDs, which deactivate to the ground state by photon emission. Acetamiprid diminishes the chemiluminescence (CL) intensity by competing with S, N-CQDs. The CL intensity reduction is proportional to the concentration of acetamiprid. S, N-CQDs were easily prepared by a hydrothermal method. Under the optimal conditions, a linear range of 2.5 - 25.0 µg L-1 with a detection limit (3σ) of 0.4 µg L-1 was obtained. This method was successfully applied to the determination of trace amounts of residual pesticides in water samples.

A sensitive turn-off-on fluorometric sensor based on S,N co-doped carbon dots for environmental analysis of Hg(II) ion.

A simple and sensitive fluorescence turn-off-on sensor was established by means of S,N co-doped carbon dots (S,N-CDs) and Ag nanoparticles (AgNPs) for the determination of Hg2+ . For this purpose, blue emissive S,N-CDs were hydrothermally synthesized and characterized using transmission electron microscopy, Fourier transform infrared spectroscopy, and energy dispersive X-ray spectroscopy. We observed that the fluorescence intensity of the as-prepared S,N-CDs was impressively quenched by AgNPs. The quenching mechanism was studied and attributed to nanosurface energy transfer and the inner filter effect between S,N-CDs and AgNPs. Furthermore, by adding Hg2+ , the fluorescence intensity of S,N-CDs/AgNPs was restored as a result of aggregation of AgNPs in the presence of Hg2+ . Based on these facts, S,N-CDs and AgNPs were exploited to design a sensitive turn-off-on sensor for analysis of Hg2+ . The recovered fluorescence signal was proportional to the concentration of Hg2+ in the range 1.5-2000 nM with a detection limit of 0.51 nM. The established sensor was used with satisfactory results for measurement of Hg2+ in environmental water samples.

A ratiometric fluorescence sensor for triticonazole based on the encapsulated boron-doped and phosphorous-doped carbon dots in the metal organic framework.

In this work, boron-doped carbon dots (B-CDs) with blue fluorescence and phosphorous-doped green emitting CDs (P-CDs) were encapsulated into zeolitic imidazolate framework-8 (ZIF-8) to prepare a dual-emission ratiometric fluorescence sensor for triticonazole. The B-CDs/P-CDs@ZIF-8 composite exhibited two emission peaks at 440 nm and 510 nm under a single wavelength excitation of 385 nm that respectively belong to B-CDs and P-CDs. In the presence of triticonazole, the fluorescence intensity of B-CDs remarkably declined while that of P-CDs remained unchanged. With increasing concentration of triticonazole, the fluorescence color of the ratiometric probe progressively changed from blue to green. Under the optimized conditions, B-CDs/P-CDs@ZIF-8 probe showed a high sensitivity with a linear range from 10 to 400 nM and a detection limit of 4.0 nM for triticonazole. The probe not only has an improved sensitivity through the accumulation of analyte molecules into the metal-organic framework but also has the advantages of ratiometric fluorescence measurements in terms of precision and accuracy. The applicability of the sensor was evaluated in the analysis of water and fruit juice samples.

Tensile Behavior of High-Density Polyethylene Including the Effects of Processing Technique, Thickness, Temperature, and Strain Rate.

The primary goal of this study was to investigate the monotonic tensile behavior of high-density polyethylene (HDPE) in its virgin, regrind, and laminated forms. HDPE is the most commonly used polymer in many industries. A variety of tensile tests were performed using plate-type specimens made of rectangular plaques. Several factors can affect the tensile behavior such as thickness, processing technique, temperature, and strain rate. Testing temperatures were chosen at -40, 23 (room temperature, RT), 53, and 82 °C to investigate temperature effect. Tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were obtained for all conditions. Tensile properties significantly reduced by increasing temperature while elastic modulus and ultimate tensile strength linearly increased at higher strain rates. A significant effect of thickness on tensile properties was observed for injection molding specimens at 23 °C, but no thickness effect was observed for compression molded specimens at either 23 or 82 °C. The aforementioned effects and discussion of their influence on tensile properties are presented in this paper. Polynomial relations for tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were developed as functions of temperature and strain rate. Such relations can be used to estimate tensile properties of HDPE as a function of temperature and/or strain rate for application in designing parts with this material.

An ultrasensitive chemiluminescence assay for 4-nitrophenol by using luminol-NaIO4 reaction catalyzed by copper, nitrogen co-doped carbon dots.

A chemiluminescence (CL) assay on the basis of the tremendous enhancing effect of copper and nitrogen co-doped carbon dots (Cu,N-CDs) on the luminol-NaIO4 reaction was introduced for the determination of nanomolar levels of 4-nitrophenol (4-NP). Cu,N-CDs were synthesized by a hydrothermal approach and characterized by TEM, XRD, EDX, and FTIR analysis. The potential CL mechanism was elucidated by recording the CL spectrum and by evaluating the influence of reactive oxygen species. It was found that 4-NP remarkably inhibited the luminol-NaIO4-Cu,N-CDs reaction and reduced the CL signal of the reaction. This fact was applied for developing a CL assay for 4-NP. Under the optimized conditions, 4-NP could be determined in the concentration range of 0.25 to 150 nM, with a detection limit as low as 0.06 nM. This assay was successfully exploited for the analysis of 4-NP in real environmental samples.

Terbium-to-quantum dot Förster resonance energy transfer for homogeneous and sensitive detection of histone methyltransferase activity.

The development of rapid, simple, and versatile biosensors for monitoring the activity of histone modifying enzymes (HMEs) is needed for the improvement of diagnostic assays, screening of HME inhibitors, and a better understanding of HME kinetics in different environments. Nanoparticles can play an important role in this regard by improving or complementing currently available enzyme detection technologies. Here, we present the development and application of a homogeneous methyltransferase (SET7/9) assay based on time-gated Förster resonance energy transfer (TG-FRET) between terbium complexes (Tb) and luminescent semiconductor quantum dots (QDs). Specific binding of a Tb-antibody conjugate to a SET7/9-methylated Lys4 on a histone H3(1-21) peptide substrate attached to the QD surface resulted in efficient FRET and provided the mechanism for monitoring the SET7/9 activity. Two common peptide-QD attachment strategies (biotin-streptavidin and polyhistidine-mediated self-assembly), two different QD colors (625 and 705 nm), and enzyme sensing with post- or pre-assembled QD-peptide conjugates demonstrated the broad applicability of this assay design. Limits of detection in the low picomolar concentration range, high selectivity tested against non-specific antibodies, enzymes, and co-factors, determination of the inhibition constants of the SET7/9 inhibitors SAH and (R)-PFI-2, and analysis of the co-factor (SAM) concentration-dependent enzyme kinetics of SET7/9 which followed the Michaelis-Menten model highlighted the excellent performance of this TG-FRET HME activity assay.