Photoresponsive surface molecularly imprinted polymer on ZnO nanorods for uric acid detection in physiological fluids

Co4+ in porous ZIF-67-derives intercalating-bridging adsorption of 2-reaction sites for simultaneous 2-electron transfer toward sensitive detection of uric acid

Metal-organic frameworks (MOFs) have been used to detect uric acid (UA), but still very challenging to achieve a low detection limit due to the low inferior conductivity of MOFs. Herein, three different N-doped ZIF-67-derived carbons were synthesized for the first time by one-step co-pyrolysis of 2-methylimidazole with cobalt nitrate (CN), cobalt acetate (CA) or cobalt chloride (CC) toward UA sensing. Afterwards, the cobalt nitrate-derived Co particle (Co/CN) supported by N-doped ZIF-67-derived carbon displays extremely low detection limit and high sensitivity for UA, outperformed all reported MOFs-based UA sensors. More interestingly, it was discovered that the high valence Co4+ within the Co/CN sample produced in high-acidic environment can intercalate in the frame for a bridge adsorption between two reaction sites, which boosted simultaneous 2-electron transfer, while Co3+ only allows an end-adsorption structure for one-electron transfer being the rate determining step. Furthermore, the bridge adsorption mode of UA on Co4+ -based catalyst was also verified by theoretical DFT calculations and XPS experiment. This work holds great promise for a selective and sensitive UA sensor for practical bioscience and clinic diagnostic applications while shedding lights in fundamental research for innovative designs and developments of high-sensitive electrochemical sensors.

Novel electrochemical sensing platform basing on di-functional stimuli-responsive imprinted polymers for simultaneous extraction and determination of metronidazole

A novel magnetic-controlled electrochemical sensor has been fabricated by combined photo-responsive surface molecular imprinted polymers (P-SMIPs) and electrochemical sensor. In particular, the P-SMIPs were obtained by living radical polymerization of photo-responsive functional monomer onto the magnetic Fe₃O₄ modified multi-walled carbon nanotubes nanocomposites. The magnetic glassy carbon electrode was introduced to make the anchoring and removal of P-SMIPs onto the magnetic-controlled glassy carbon electrode easy to manipulate. Driven by UV/vis light, the platform performs releasing and absorption of metronidazole basing on conformational variations of the photo-responsive monomer at the receptor sites part in the P-SMIPs. This process can be tested by the photo-responsive variations of metronidazole electrochemical signal. As the consequence, extracting of P-SMIPs sensor can be conveniently triggered by the controllable UV light intervention measure, leading to effectively improve in both analytes mass transfer rate to the receiving media and extraction efficiency. The experimental result indicated that the excellent recoveries of metronidazole were varied between 77.9% and 89.9% with RSDs ≤4.87% in the biological samples. Therefore, the P-SMIPs sensor shows satisfactory potential in reusable extractions that can be recycled several times with no significant loss of activity, and this utilization strategy can be extended to other analytes, achieving manifold applications of pharmaceutical and environmental.

A visible-light-responsive molecularly imprinted polyurethane for specific detection of dibenzothiophene in gasoline

Dibenzothiophene and its derivatives in gasoline and diesel would release sulfur oxides during combustion, and this is harmful to human health and the environment. This paper reports a method based on a visible-light-responsive molecularly imprinted polyurethane (VMIPU) to monitor trace dibenzothiophene in gasoline. The VMIPU was prepared by a polyaddition reaction using N,N-bis-(2-hydroxyethyl)-4-phenylazoaniline as the functional monomer, dibenzothiophene as the template molecule, diphenylmethane diisocyanate as the crosslinker and castor oil as the chain extender. The VMIPU showed good visible-light-response and specific adsorption for dibenzothiophene. The trans → cis photoisomerization rate constant of azobenzene chromophores in the VMIPU shows a linear relationship with the dibenzothiophene concentration in the range of 0-20 μmol L^-1. This was used to estimate trace dibenzothiophene in spiked gasoline with recoveries of 95.7-101.0% and relative standard deviations of 7.0-12.7%.

Molecular Imprinting Technology for Determination of Uric Acid

The review focuses on the overview of electrochemical sensors based on molecularly imprinted polymers (MIPs) for the determination of uric acid. The importance of robust and precise determination of uric acid is highlighted, a short description of the principles of molecular imprinting technology is presented, and advantages over the others affinity-based analytical methods are discussed. The review is mainly concerned with the electro-analytical methods like cyclic voltammetry, electrochemical impedance spectroscopy, amperometry, etc. Moreover, there are some scattered notes to the other electrochemistry-related analytical methods, which are capable of providing additional information and to solve some challenges that are not achievable using standard electrochemical methods. The significance of these overviewed methods is highlighted. The overview of the research that is employing MIPs imprinted with uric acid is mainly targeted to address these topics: (i) type of polymers, which are used to design uric acid imprint structures; (ii) types of working electrodes and/or other parts of signal transducing systems applied for the registration of analytical signal; (iii) the description of the uric acid extraction procedures applied for the design of final MIP-structure; (iv) advantages and disadvantages of electrochemical methods and other signal transducing methods used for the registration of the analytical signal; (vi) overview of types of interfering molecules, which were analyzed to evaluate the selectivity; (vi) comparison of analytical characteristics such as linear range, limits of detection and quantification, reusability, reproducibility, repeatability, and stability. Some insights in future development of uric acid sensors are discussed in this review.

A hollow visible-light-responsive surface molecularly imprinted polymer for the detection of chlorpyrifos in vegetables and fruits

A visible-light-responsive azobenzene derivative, 3,5-dichloro-4-((2,6-dichloro-4-(methacryloyloxy)phenyl)diazenyl)benzoic acid, was synthesized and used as the functional monomer to fabricate a visible-light-responsive core-shell structured surface molecularly imprinted polymer (PS-co-PMAA@VSMIP). After removal of the sacrificial PS-co-PMAA core, a hollow structured surface molecularly imprinted polymer (HVSMIP) was obtained. Both the PS-co-PMAA@VSMIP and HVSMIP were used for the detection of chlorpyrifos, a moderately toxic organophosphate pesticide. They exhibited good visible-light-responsive properties (550 nm for trans→cis and 440 nm for cis→trans isomerization for an azobenzene chromophore) in ethanol/water (9:1, v/v). Compared with the PS-co-PMAA@VSMIP, the HVSMIP had a larger surface area, pore volume, binding capacity, imprinting effect, maximum chemical binding capacity, dissociation constant, and photo-isomerization rate. The HVSMIP was applied to detect trace chlorpyrifos in fruit and vegetable samples. This was achieved by measuring the trans→cis rate constant of the HVSMIP in the sample solution, with good recoveries, low relative standard deviations, and a low detection limit.

Selective enrichment-release of trace dibutyl phthalate via molecular-imprinting based photo-controlled switching followed by high-performance liquid chromatography analysis

A novel intelligent photo-controlled molecularly imprinted polymers were synthesized, based on the magnetic core-shell structure, with 4-[(4-methacryloyloxy) phenylazo] benzenesulfonic acid as the functional monomer and ethylene glycol dimethyl acrylate as the cross-linking agent. Subsequently, a series of light-controlled enrichment-release performance showed that it only took about 30 and 10 min to reach the equilibrium photosensitive characteristic peak, respectively. The photo-controlled polymers could intelligently select target molecules, the maximum adsorption capacity for dibutyl phthalate was 3.88 mg/g. However, the adsorption capacity for its structural analogue dicyclohexyl phthalate was only 0.88 mg/g. The Freundlich and Langmuir isothermal equations were discussed for the specific enrichment process. Finally, the photo-controlled molecularly imprinted polymers were successfully applied to the selective detection of dibutyl phthalate, with the recovery rate of 95.4-98.4%. It could be used for the analysis of trace dibutyl phthalate in actual samples.

Photoresponsive Surface Molecularly Imprinted Polymers for the Detection of Profenofos in Tomato and Mangosteen

As a moderately toxic organophosphorus pesticide, profenofos (PFF) is widely used in agricultural practice, resulting in the accumulation of a high amount of PFF in agricultural products and the environment. This will inevitably damage our health. Therefore, it is important to establish a convenient and sensitive method for the detection of PFF. This paper reports a photoresponsive surface-imprinted polymer based on poly(styrene-co-methyl acrylic acid) (PS-co-PMAA@PSMIPs) for the detection of PFF by using carboxyl-capped polystyrene microspheres (PS-co-PMAA), PFF, 4-((4-(methacryloyloxy)phenyl)diazenyl) benzoic acid, and triethanolamine trimethacrylate as the substrate, template, functional monomer, and cross-linker, respectively. PS-co-PMAA@PSMIP shows good photoresponsive properties in DMSO/H2O (3:1, v/v). Its photoisomerization rate constant exhibits a good linear relationship with PFF concentration in the range of 0~15 μmol/L. PS-co-PMAA@PSMIP was applied for the determination of PFF in spiked tomato and mangosteen with good recoveries ranging in 94.4-102.4%.

Two different states conversion mechanism of the imprinting sites

Bisphenol A molecular imprinted adsorbent (BMIA) was successfully synthesized by a sol-gel process and showed a good specific binding performance in the water. The further studies showed that the mass transfer process was controlled by in-diffusion, and the synthesis conditions would effect on the amount of imprinting sites. Scatchard model analysis evidenced that the high binding affinity sites and the low binding affinity sites were both on BMIA, and the high binding affinity sites played a key role in the specific binding process. Scatchard model analysis of temperature effect experiments and dosage effect experiments proved that the specific binding sites with high binding affinity and the unexpressed specific binding sites with low binding affinity were the two different states of the imprinting binding sites. The conversion between the two different states depended on the reaction driving force, and the increasing reaction driving force would increase the number of specific binding sites. Especially, the temperature showed a linear positive correlation with the amount of specific binding sites. Finally, a possible model was put forward to explain the two different states conversion mechanism of the imprinting sites.

A photoresponsive molecularly imprinted polymer with rapid visible-light-induced photoswitching for 4-ethylphenol in red wine

The trans to cis isomerization of the azobenzene chromophore in most azobenzene-based photoresponsive molecularly imprinted polymers (MIPs) is initiated by UV irradiation. This limits the application of these materials in cases where UV light toxicity is an issue, such as in biological systems, food monitoring, and drug delivery. Herein we report a tetra-ortho-methyl substituted azobenzene, (4-[(4-methacryloyloxy)-2,6-dimethyl phenylazo]-3,5-dimethyl benzenesulfonic acid (MADPADSA). The photoswitching of MADPADSA could be induced by visible-light irradiation (550 nm for trans to cis and 475 nm for cis to trans) in 4-hydroxyethylpiperazineethanesulfonic acid (HEPES) buffer-ethanol (4:1, v/v) at pH 7.0, however, the photoisomerization was slow. With the use of MADPADSA as a functional monomer, NaYF₄:Yb³⁺,Er³⁺ as a substrate, 4-ethylphenol (4-EP) as a template, a novel photoresponsive surface molecularly imprinted polymer NaYF₄:Yb³⁺,Er³⁺@MIP was obtained. The NaYF₄:Yb³⁺,Er³⁺@MIP displayed rapid visible-light-induced photoswitching. The NaYF₄:Yb³⁺,Er³⁺ substrate could efficiently increase the trans to cis isomerization rate of the photoresponsive MIP on its surface, which was faster than that of the corresponding azobenzene monomer MADPADSA. Possible reasons for this effect were investigated by fluorescence spectroscopy. NaYF₄:Yb³⁺,Er³⁺@MIP displayed good specificity toward 4-EP with a specific binding constant (K_d) of 3.67 × 10^-6 mol L^-1 and an apparent maximum adsorption capacity (Q_max) of 10.73 μmol g^-1, respectively. NaYF₄:Yb³⁺,Er³⁺@MIP was applied to determine the concentration of 4-EP in red wine with good efficiency and a limit of detection lower than the value that could cause an unpleasant off-flavor.

Electrochemical preparation of surface molecularly imprinted poly(3-aminophenylboronic acid)/MWCNTs nanocomposite for sensitive sensing of epinephrine

A nanocomposite with multi-walled carbon nanotubes (MWCNTs) coated with surface molecularly imprinted polymers (MIPs) poly(3-aminophenylboronic acid) (PAPBA) was successfully prepared via potentiodynamic electropolymerization and tested as an effective electrochemical material for epinephrine (EP) detection. The morphology and properties of the sensing material were characterized with scanning electron microscopy and electrochemical impedance spectroscopy. Compared with MWCNTs or non-imprinted polymers PAPBA modified MWCNTs electrodes, the PAPBA(MIPs)/MWCNTs modified electrode showed a lower charge transfer resistance and enhanced electrochemical performance for EP detection. The improved performance can be attributed to the large amount of specific imprinted cavities with boric acid group which can selectively adsorb EP molecule and the synergistic effect between MWCNTs and PAPBA(MIPs). The effects of pH, the molar ratio between monomer and template molecule, the cycle number of electropolymerization, and the accumulation time of the modified electrode on the sensing performance were investigated. It was found that under the optimal conditions, the PAPBA(MIPs)/MWCNTs sensor could effectively recognize EP from many possible interferents of higher concentration within a wide linear range of 0.2-800 μmol·L^-1, with low detection limit of 35 nmol·L^-1, high sensitivity and good discrimination. The detection of EP in human serum and real injection samples using the PAPBA(MIPs)/MWCNTs sensor also gave satisfactory results.

Imprinted Oxide and MIP/Oxide Hybrid Nanomaterials for Chemical Sensors †

The oxides of transition, post-transition and rare-earth metals have a long history of robust and fast responsive recognition elements for electronic, optical, and gravimetric devices. A wide range of applications successfully utilized pristine or doped metal oxides and polymer-oxide hybrids as nanostructured recognition elements for the detection of biologically relevant molecules, harmful organic substances, and drugs as well as for the investigative process control applications. An overview of the selected recognition applications of molecularly imprinted sol-gel phases, metal oxides and hybrid nanomaterials composed of molecularly imprinted polymers (MIP) and metal oxides is presented herein. The formation and fabrication processes for imprinted sol-gel layers, metal oxides, MIP-coated oxide nanoparticles and other MIP/oxide nanohybrids are discussed along with their applications in monitoring bioorganic analytes and processes. The sensor characteristics such as dynamic detection range and limit of detection are compared as the performance criterion and the miniaturization and commercialization possibilities are critically discussed.

A facile fluorescence assay for rapid and sensitive detection of uric acid based on carbon dots and MnO2nanosheets

A sensitive turn-on fluorescence method for uric acid detection is proposed based on FRET between carbon dots and MnO₂nanosheets.

Nanosized Difunctional Photo Responsive Magnetic Imprinting Polymer for Electrochemically Monitored Light-Driven Paracetamol Extraction

Herein, a novel photoresponsive magnetic electrochemical imprinting sensor for the selective extraction of paracetamol from biological samples was designed. In particular, nanosized photoresponsive molecular imprinted polymers were prepared on the surface of magnetic Fe₃O₄ nanoparticles through living radical polymerization of azobenzene. The introduction of a magnetic-controlled glassy carbon electrode makes the immobilization and removal of nanosized photoresponsive molecular imprinted polymers on the magnetic-controlled glassy carbon electrode surface facilely operational. With the photoresponsive property, the sensor undergoes reversible release and uptake of paracetamol upon alternative irradiation at 365 and 440 nm basing on a configurational change of azobenzene monomer in the photoresponsive molecular imprinted polymers receptor sites. Simultaneously, these processes are monitored by the photoresponsive changes of electrochemical signal from paracetamol. Two linear ranges from 0.001 to 0.7 mmol L^-1 (R² = 0.96) and 0.7 to 7 mmol L^-1 (R² = 0.95) for paracetamol determination were obtained with a quantification limit of 0.000 86 mmol L^-1 and a detection limit of 0.000 43 mmol L^-1. The recoveries of paracetamol in the urine as determined by photoresponsive molecular imprinted polymers extraction were varied between 87.5% and 93.3%. As a consequence, combining photocontrolled selective extraction, interfacial stability from magnetic adsorption, and specifically electrochemical response, the photoresponsive molecular imprinted polymers sensor shows significant advantages for simultaneous separation, enrichment, and detection of trace paracetamol in biological samples.

Antibacterial SnO2 nanorods as efficient fillers of poly(propylene fumarate-co-ethylene glycol) biomaterials

Antibacterial and biocompatible SnO₂ nanorods have been easily synthesized through a hydrothermal process with the aid of a cationic surfactant, and incorporated as nanoreinforcements in poly(propylene fumarate-co-ethylene glycol) (P(PF-co-EG)) copolymer crosslinked with N-vinyl-pyrrolidone (NVP) by sonication and thermal curing. The nanorods were randomly and individually dispersed inside the P(PF-co-EG) network, and noticeably increased the thermal stability, hydrophilicity, degree of crystallinity, protein absorption capability as well as stiffness and strength of the matrix, whilst decreased its level of porosity and biodegradation rate. More importantly, the resulting nanocomposites retained adequate rigidity and strength after immersion in a simulated body fluid (SBF) at 37°C. They also exhibited biocide action against Gram-positive and Gram-negative bacteria; their antibacterial effect was strong under UV-light illumination whilst in dark conditions was only moderate. Further, they did not cause toxicity on human dermal fibroblasts. The friction coefficient and wear rate strongly decreased with increasing nanorod loading under both dry and SBF conditions; the greatest drops in SBF were about 18-fold and 13-fold, respectively, compared to those of the copolymer network. These novel biomaterials are good candidates to be applied in the field of soft-tissue engineering.