Phosphorimetric determination of 4-nitrophenol using mesoporous molecular imprinting polymers containing manganese(II)-doped ZnS quantum dots

Nitrophenols in the environment: An update on pretreatment and analysis techniques since 2017

Nitrophenols, a versatile intermediate, have been widely used in leather, medicine, chemical synthesis, and other fields. Because these components are widely applied, they can enter the environment through various routes, leading to many hazards and toxicities. There has been a recent surge in the development of simple, rapid, environmentally friendly, and effective techniques for determining these environmental pollutants. This review provides a comprehensive overview of the latest research progress on the pretreatment and analysis methods of nitrophenols since 2017, with a focus on environmental samples. Pretreatment methods include liquid-liquid extraction, solid-phase extraction, dispersive extraction, and microextraction methods. Analysis methods mainly include liquid chromatography-based methods, gas chromatography-based methods, supercritical fluid chromatography. In addition, this review also discusses and compares the advantages/disadvantages and development prospects of different pretreatment and analysis methods to provide a reference for further research.

Preparation of room-temperature phosphorescence-ratiometric fluorescence magnetic mesoporous imprinted microspheres and its application in detection of malachite green and tartrazine in multimatrix

The photoluminescent properties of Mn-doped ZnS quantum dots were fully exploited, and room-temperature phosphorescence (RTP)-ratiometric fluorescence (RF) magnetic mesoporous molecularly imprinted polymers (PFMM-MIPs) were prepared by integrating molecular imprinting technology. RTP was used to detect malachite green (MG). The fluorescence at 420 nm and the peak at 590 nm in the fluorescence mode were used as the response reference signals respectively to detect tartrazine (TZ). The linear responsive range and detection limit of MG were 0.01-150 μM and 4.3 nM, and these of TZ were 0.05-80 μM and 23.7 nM. RTP, which can avoid the interference of background fluorescence, and RF with self-calibration ability can both largely weaken the matrix effect. This work enables single-probe-type MIPs to achieve dual-target analysis via RTP and RF. This method provides excellent sensitivity, specificity, recovery and recyclability, and is expected to be prospectively applied in the fields of food, environment and biological analyses.

A mesoporous silica-based probe with a molecularly imprinted polymer recognition and Mn:ZnS QDs@rhodamine B ratiometric fluorescence sensing strategy for the analysis of 4-nitrophenol

In this study, a mesoporous silica fluorescence probe co-doped with manganese-doped zinc sulfide quantum dots (Mn:ZnS QDs) and rhodamine B (RB) and coated with molecularly imprinted polymer (MIP) has been prepared by sol-gel methods. The morphology and structure were characterized in detail by transmission electron microscopy (TEM), Fourier transform-infrared absorption spectroscopy (FT-IR) and ultraviolet-visible absorption spectroscopy (UV-vis). The probe exhibited two characteristic emission peaks at 411 nm and 582 nm, and the synchronous ratiometric fluorescence responses F₄₁₁/F₅₈₂ to different concentrations of 4-nitrophenol (4-NP) showed a good linear correlation in the range of 0.01-10 μmol L^-1 besides achieving the sensitive detection of 4-NP with a detection limit as low as 3.0 nmol L^-1 (3σ). The probe possesses the advantages of selectivity toward the target molecular structure, self-stability in the detection time domain and anti-interference ability, exhibiting excellent potential for application in 4-NP detection in different water environments.

Pre-Anodized Graphite Pencil Electrode Coated with a Poly(Thionine) Film for Simultaneous Sensing of 3-Nitrophenol and 4-Nitrophenol in Environmental Water Samples

A very simple, as well as sensitive and selective, sensing protocol was developed on a pre-anodized graphite pencil electrode surface coated using poly(thionine) (APGE/PTH). The poly(thionine) coated graphite pencil was then used for simultaneous sensing of 3-nitrophenol (3-NP) and 4-nitrophenol (4-NP). The poly(thionine) coated electrode exhibited an enhanced electrocatalytic property towards nitrophenol (3-NP and 4-NP) reduction. Redox peak potential and current of both nitrophenols were found well resolved and their simultaneous analysis was studied. Under optimized experimental conditions, APGE/PTH showed a long linear concentration range from 20 to 230 nM and 15 nM to 280 nM with a calculated limit of detection (LOD) of 4.5 and 4 nM and a sensitivity of 22.45 µA/nM and 27.12 µA/nM for 3-NP and 4-NP, respectively. Real sample analysis using the prepared sensor was tested with different environmental water samples and the sensors exhibited excellent recovery results in the range from 98.16 to 103.43%. Finally, the sensor exposed an promising selectivity, stability, and reproducibility towards sensing of 3-NP and 4-NP.

Graphene/fluorescein dye-based sensor for detecting As(III) in drinking water

A complex of reduced graphene oxide (rGO) and fluorescein (FL) dye nanoparticles of size between 50 and 100 nm has been prepared and its sensing performance for detection of As(III) in drinking water has been reported. When As(III) binds to the rGO-FL nanoparticles the relative quenching of fluorescence was increased with increase in As(III) concentration thus provide two linear calibration ranges (0-4.0 mmol L-1 and 4.0-10 mmol L-1). The fluorescence quenching mechanism was investigated by using time-resolved fluorescence spectroscopy and molecular modeling. The detection limit of this sensor has been determined as equal to 0.96 µg L-1 which is about 10 times lower than the WHO stipulated standard for As(III) in drinking water (10 µg L-1). The analytical performance and potential application of the nanosensor was compared to commercial field kits used in arsenic monitoring. The sensor proposed in this study is fast, sensitive and accurate for detection of As(III) in drinking water and environmental samples.

A novel magnetic fluorescent molecularly imprinted sensor for highly selective and sensitive detection of 4-nitrophenol in food samples through a dual-recognition mechanism

In this study, surface imprinting, magnetic separation, and fluorescent detection were integrated to develop a dual-recognition sensor (MF-MIPs), which was used for highly selective and sensitive detection of 4-nitrophenol (4-NP) in food samples. Silane-functionalized carbon dots (Si-CDs) participated in the imprinting process and were uniformly distributed into the MIPs layers. MF-MIPs sensor exhibited a high fluorescence response and selectivity based on the dual-recognition mechanism of imprinting recognition and fluorescence identification. The relative fluorescence intensity of MF-MIPs sensor presented a good linear relationship in the range of 0.08-10 μmol·L^-1 with a low limit of detection (23.45 nmol·L¹) for 4NP. MF-MIPs sensor showed high anti-interference, as well as excellent stability and reusability. The 4-NP recovery from spiked food samples ranged from 93.20 to 102.15%, and the relative standard deviation was lower than 5.0%. Therefore, MF-MIPs sensor may be a promising method for 4-NP detection in food samples.

Nitrogen, silicon co-doped carbon dots as the fluorescence nanoprobe for trace p-nitrophenol detection based on inner filter effect

P-nitrophenol (PNP) has been widely applied to industry processing for many purposes, but the persistence and toxicity of residuum may pose risks to human health. To analyze PNP in industrial and agricultural wastewater, a versatile fluorescent probe sensing platform was proposed. In this work, we devised a fluorescence approach that utilized nitrogen, silicon co-doped carbon dots (N,Si-CDs) to monitor PNP originating from the inner filter effect (IFE). The N,Si-CDs were generated in a one-step hydrothermal synthesis, and which possessed outstanding fluorescence signal and water-dispersity. Emission at 441 nm was monitored with excitation at 360 nm using a common spectrofluorometer. The method achieved an exceptionally low limit of detection (LOD) of 0.011 μM. Furthermore, this method not only eliminates the interference from metal ions and acid ions, but also provides a potential application prospect for N,Si-CDs in the field of water monitoring. Analysis of tap and lake water led to 93.30-106.30% recoveries and <1% relative standard deviation at 2.5-25 μM PNP concentrations.

A review of the incorporation of QDs and imprinting technology in optical sensors – imprinting methods and sensing responses

This review aims to cover the simultaneous method of using molecularly imprinted technology and quantum dots (QDs) as well as its application in the field of optical sensors.

Smart materials for point-of-care testing: From sample extraction to analyte sensing and readout signal generator

The last decade has seen a surge of technical developments in the field on point-of-care testing (POCT). While these developments are extremely diverse, the common aim is to implement improved methods for quick, reliable and inexpensive diagnosis of patients within the clinical setting. While examples of successful introduction and use of POCT techniques are growing, further developments are still necessary to create POCT devices with better portability, usability and performance. Advances in smart materials emerge as potentially valuable know-hows to provide a competitive edge to the development of next generation POCT devices. This review describes the key advantages of adopting smart material-based technologies at different analytical stages of a POCT platform. Under these analytical stages which involves sample pre-treatment, analyte sensing and readout signal generator, several concepts and approaches from contemporary research work in using smart material-based technologies will be the major focus in this review. Lastly, challenges and potential outlook in implementing materials technologies from the application point of view for POCT will be discussed.

4-nitrophenol optical sensing with N doped oxidized carbon dots

In this work, we report a facile strategy for 4-nitrophenol (4-NP) sensing using highly luminescent nitrogen-doped oxidized carbon dots. The quenching of fluorescence (turn OFF), with the addition of trace amounts of organic pollutant (4-NP) in NOCDs, has been attributed to the complete reduction of nitrogen-doped oxidized carbon dots (NOCDs) to reduced nitrogen-doped oxidized carbon dots (rNOCDs) and its formation was confirmed by infrared, X-ray diffraction and X-ray photoelectron spectroscopy measurements. The chemical changes in oxygen-containing functional groups of NOCDs, in the presence of 4-NP, are elucidated and corresponding characterization through XPS reveals the changes in the peak intensities of CC (284.5 eV) and OCO (288.6 eV), indicating a decrement in hydroxyl groups that hinder its complete reduction to NOCDs. The sensitivity of NOCDs towards 4-NP has been tested in spiked tap water in the concentration range 2 μM to 2 mM with the minimum detection limit of 2 μM (linear detection range from 2 to 100 μM with regression coefficient R² =0.99). The proposed simple sensing platform can be used to reduce NOCDs and simultaneously sense low concentrations of 4-NP. Finally, an effective treatment to improve the reduction of nitrogen-doped graphene oxide is proposed.

Molecularly imprinted polymer containing fluorescent graphene quantum dots as a new fluorescent nanosensor for detection of methamphetamine

A novel fluorescent nanosensor based on graphene quantum dots embedded within molecularly imprinted polymer (GQDs@MIP) was developed for detection and determination of methamphetamine (METH). The resulting GQDs@MIP nanocomposite exhibited higher methamphetamine selectivity in comparison with corresponding non-imprinted polymer (GQDs@NIP). Characterization of the GQDs@MIP nanocomposite was done by nitrogen adsorption and desorption analysis (BET method), transmission electron microscopy (TEM), photoluminescence (PL), ultraviolet-visible (UV-Vis), and Fourier transform infrared (FT-IR) spectroscopies. The fluorescence intensity of GQDs@MIP was efficiently quenched in the presence of methamphetamine template molecules while no quenching was observed in the presence of other analytes such as amphetamine, ibuprofen, codeine, and morphine. Using this method, the detection limit of 1.7 μg/L was obtained for methamphetamine determination.

Selective and sensitive determination of celastrol in traditional Chinese medicine based on molecularly imprinted polymers modified Mn-doped ZnS quantum dots optosensing materials

In this work, we proposed a facile strategy to prepare molecularly imprinted polymers (MIPs) modified Mn-doped ZnS quantum dots (QDs) as optosensing materials via sol-gel polymerization for specific recognition of celastrol (Cel) in traditional Chinese medicine (TCM). Firstly, L-Cysteine (L-Cys) modified Mn-doped ZnS QDs (L-Cys@Mn-ZnS) was used as imprinting substrate. The amino and carboxyl groups on the surface of Mn-ZnS QDs can provide more binding sites for imprinting polymerization. Then, the fluorescent MIPs was synthesized in the presence of L-Cys@Mn-ZnS QDs, template celastrol, 3-aminopropyl triethoxysilane (APTES) and ammonium hydroxide in the ethanol-water (9/1, v/v) solution. The morphology and structure of the products were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometer (XRD) and X-ray photoelectron spectroscopy (XPS). The resulting MIPs functionalized Mn-doped ZnS QDs (denoted as MIPs@L-Cys@Mn-ZnS QDs) had higher imprinting factor of 14.19 and significant selectivity. The MIPs@L-Cys@Mn-ZnS QDs as fluorescent probe exhibited sensitive response to Cel in the linear range from 0.1 μM to 3.5 μM and the limit of detection was estimated to be 35.2 nM. The probe was also applied for the detection of Cel in traditional Chinese medicine with recovery ranged from 88.0%-105.0%. The results confirmed that MIPs@L-Cys@Mn-ZnS QDs could efficiently and specifically capture Cel from actual complex traditional Chinese medicine samples.

A label-free RTP sensor based on aptamer/quantum dot nanocomposites for cytochrome c detection

Given the outstanding room-temperature phosphorescence (RTP) of Mn–ZnS quantum dots (QDs) and the specific recognition performance of the aptamer, we built phosphorescent composites from aptamers conjugated with polyethyleneimine quantum dots (PEI-QDs) and applied them to cytochrome c (Cyt c) detection. Specifically, QDs/CBA composites were generated from the electrostatic interaction between the positively-charged PEI-QDs and the negatively-charged Cyt c binding aptamer (CBA). With the presence of Cyt c, the Cyt c can specifically bind with the QDs/CBA composites, and quench the RTP of QDs through photoinduced electron-transfer (PIET). Thereby, an optical biosensor for Cyt c detection was built, which had a detection range of 0.166–9.96 μM and a detection limit of 0.084 μM. This aptamer-mediated phosphorescent sensor with high specificity and operational simplicity can effectively avoid the interference of scattering light from complex substrates. Our findings offer a new clue for building biosensors based on QDs and aptamers.

In this study, the nanocomposites from polyethyleneimine-capped Mn-doped ZnS QDs (PEI-QDs) and Cyt c binding aptamer (CBA) were prepared and used as Cyt c RTP sensors..