► A caffeic acid (CA) MIP has been synthesised in the form of well-defined microspheres. ► Bath rebinding studies demonstrated high imprinting phenomenon. ► The MIP was packed into a HPLC column ...allowing selective recognition of CA over 8 related compounds. ► The MIP-column enabled the efficient removal of CA from apple juice samples.
In the current work, a molecularly imprinted polymer (MIP) has been synthesised and used to enable the extraction of a naturally-occurring antioxidant from complex media. More specifically, we describe the first example of a caffeic acid (CA) MIP which has been synthesised in the form of well-defined polymer microspheres, and its use for the extraction of CA from fruit juice sample. The CA MIP was synthesised by precipitation polymerisation using 4-vinylpyridine as functional monomer, divinylbenzene-80 as crosslinker and acetonitrile:toluene (75/25, v/v) as porogen. The particle sizing and morphological characterisation of the polymers was carried out by means of scanning electron microscopy (narrow particle size distribution; ∼5 and 1.5
μm particle diameters for the MIP and NIP non-imprinted polymer, respectively) and nitrogen sorption porosimetry (specific surface areas of 340 and 350
m
2
g
−1, and specific pore volumes of 0.17 and 0.19
cm
3
g
−1 for the MIP and NIP, respectively). The polymers were evaluated further by batch rebinding experiments, and from the derived isotherms their binding capacity and binding strength were determined (number of binding sites (
N
K
)
=
0.6 and 0.3
mmol
g
−1 for the MIP and NIP, respectively, and apparent average adsorption constant (
K
N
)
=
10.0 and 1.6
L
mmol
−1 for the MIP and NIP, respectively). To evaluate the molecular recognition character of the MIP it was packed into a stainless steel column (50
mm
×
4.6
mm i.d.) and evaluated as an HPLC-stationary phase. The mobile phase composition, flow rate, and the elution profile were then optimised in order to improve the peak shape without negatively affecting the imprinting factor (
IF). Very interesting, promising properties were revealed. The imprinting factor (
IF) under the optimised conditions was 11.9. Finally, when the imprinted LC column was used for the selective recognition of CA over eight related compounds, very good selectivity was obtained. This outcome enabled the direct extraction of CA in commercial apple juice samples with recoveries in excess of 81% and, rather significantly, without any need for a clean-up step prior to the extraction.
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•A method for optimally combining multifrequency information in phase-resolved luminescence spectroscopy is proposed.•Rectangular-wave signals are used to improve the accuracy in the ...determination of the analyte concentration.•An estimation on-the-fly of uncertainties associated with measurements is possible.•The proposed method has been applied to an oxygen measuring system.
A method for optimally combining multifrequency information in phase-resolved luminescence spectroscopy using rectangular-wave signals is proposed to improve the accuracy in the determination of the analyte concentration. From the rectangular-wave signal, phase-shift- and modulation-factor-based apparent lifetimes are estimated at each harmonic independently, together with their corresponding standard errors. Both the lifetimes and their standard errors are estimated “on-the-fly” from the Fast Fourier Transform (FFT) of the excitation and emission signals and applying error propagation theory. Independent determinations of the analyte concentration and their standard errors are then optimally combined in order to obtain an improved determination of the analyte concentration. The combination, formulated in a statistical framework, is a weighted average of different determinations proportional to the inverse of the variance of each independent determination. The proposed method has been applied to an oxygen measuring system to evaluate its accuracy and demonstrate its applicability in real-time measuring instruments.
Hydrothermal synthesis is a chemical process that has gained much interest in recent years, especially for the synthesis of LiFePO4 since it is a method that requires a relatively low temperature, ...short reaction time, and it is reproducible. In this work, LiFePO4 microparticles have been synthesized by means of a fast heating system (sand bath) under hydrothermal conditions. The experiments have been carried out under two different heating rates (86 °C/min and 5.26 °C/min), two different residence times (5 and 30 min), and two different cooling rates (−455 °C/min and −8 °C/min). The effects that these three parameters had on the synthesized particles were verified using several techniques such as X-ray diffraction and scanning electron microscopy. It was observed that the heating rate had a great influence on the purity, crystallization, and morphology of the synthesized LiFePO4 particles. In addition, the high influence of cooling rate on the crystallization and morphology of the particles was also analyzed.
Abstract Herein, a new electrochemical sensing system based on lutetium copper nanoparticles supported on hexagonal boron nitride (Lu‐Cu@h‐BN) was designed for the sensitive detection of ...ciprofloxacin (CIP) antibiotic. A simple hydrothermal method was used to synthesize the nanocomposite. The structural and morphological characteristics of the as‐prepared nanocomposite were investigated using various analytical techniques such as Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction (XRD), scanning electron microscopy (SEM), and X‐ray photoelectron spectroscopy (XPS). The newly developed Lu‐Cu@h‐BN nanocomposite was used as an electrode modifier for sensing and signalling of CIP. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used to study the electrochemical activities of the bare GCE, Cu‐h‐BN/GCE, Lu‐h‐BN/GCE, Lu‐Cu/GCE, and Lu‐Cu@h‐BN/GCE. The electro‐oxidation of CIP on electrode surface exhibited an irreversible, diffusion‐controlled process. The sensor system obtained a wider linear range of (0.05–100 μM) with a lower detection limit value of 0.03 μM and sensitivity 0.7443 μA μM −1 cm −2 . Furthermore, the sensor demonstrated an excellent selectivity, good stability, and reproducibility, with acceptable recoveries of 96 % to 104 % in real water sample analysis.
In Vitro Oxygen Sensing Using Intraocular Microrobots Ergeneman, Olgaç; Nelson, Bradley J.; Chatzipirpiridis, George ...
IEEE transactions on biomedical engineering,
11/2012, Letnik:
59, Številka:
11
Journal Article
Recenzirano
We present a luminescence oxygen sensor integrated with a wireless intraocular microrobot for minimally-invasive diagnosis. This microrobot can be accurately controlled in the intraocular cavity by ...applying magnetic fields. The microrobot consists of a magnetic body susceptible to magnetic fields and a sensor coating. This coating embodies Pt(II) octaethylporphine (PtOEP) dyes as the luminescence material and polystyrene as a supporting matrix, and it can be wirelessly excited and read out by optical means. The sensor works based on quenching of luminescence in the presence of oxygen. The excitation and emission spectrum, response time, and oxygen sensitivity of the sensor were characterized using a spectrometer. A custom device was designed and built to use this sensor for intraocular measurements with the microrobot. Due to the intrinsic nature of luminescence lifetimes, a frequency-domain lifetime measurement approach was used. An alternative sensor design with increased performance was demonstrated by using poly(styrene-co-maleic anhydride) (PS-MA) and PtOEP nanospheres.
We report the fabrication of optical oxygen sensor films using electrophoretic deposition (EPD) of poly(styrene-co-maleic anhydride) nanoparticles containing the oxygen-sensitive dye platinum(ii) ...meso-tetra(pentafluorophenyl)porphine. Compared to other deposition methods, the EPD is simple and allows easy control over deposition, which is crucial for the implementation of optical sensing films in microdevices. By optimizing the synthesis of the functional nanoparticles, anodic EPD can be performed. The amount of deposited particles can be tuned by varying either the electrical potential or the deposition time. The sensing phases were characterized using a phase-modulation technique showing a Stern-Volmer constant (kSV1) between 45 and 52 bar(-1) for gas and of 20.72 bar(-1) in the aqueous phase without leaching of the particles from the surface. The small thickness of the layers lead to short response times (<0.4 s). This is the first time that polymeric optical sensing films have been obtained by EPD from dispersions of oxygen sensing nanoparticles.
To enhance the advantages of fluorescent flow-through sensing for drinking water we have designed a novel sensing matrix based on molecularly imprinted polymers (MIPs). The synergic combination of a ...tailor-made MIP recognition with a selective room temperature fluorescence detection is a novel concept for optosensing devices and is assessed here for the simple and selective determination of pollutants in water.
We describe a simple approach to preparing synthetic receptors for monoamine naphthalene compounds (MA-NCs) using non-covalent molecular imprinting techniques and naphthalene as template. We examine in detail the binding characteristics of the imprinted polymer and describe the flow-through sensor of MA-NCs by solid-surface fluorescence. Its detection limits for recognizing 1-naphthylamine (1-NA) and 2-naphthylamine (2-NA) separately are 26ngmL−1 and 50ngmL−1, respectively, and it also determines 1-NA and 2-NA simultaneously with a detection limit of 45ngmL−1.
All the instrumental, chemical and flow variables were carefully optimized and an interference study was carried out to demonstrate its applicability and selectivity. Finally, we applied it to the analysis of 1-NA and 2-NA in tap and mineral waters, obtaining a 98% average recovery rate.
In this study, a novel phosphorescent Ir(III) complex Ir(2-phenylpyridine)2(4,4'-bis(2-(4-N,N-methylhexylaminophenyl)ethyl)-2-2'-bipyridine)Cl (for convenience, the complex was given the synonym ...N-948) has been designed and synthesized, to be used as an oxygen probe. It was characterized by spectroscopic and analytical methods when incorporated in a polystyrene and nanostructured metal oxide support. N-948 is the first Ir complex in the literature with a luminescence emission at a wavelength higher than 650 nm (665 nm), with a quantum yield higher than 0.50 (0.58 +/- 0.05) and an extremely long phosphorescence lifetime (102 micros) which has been used for developing oxygen-sensitive films. In addition, the new complex shows a Stern-Volmer constant which is 20 times higher than that of other Ir complexes known from the literature when they are immobilized in polystyrene. The sensing film shows long-term stability (up to 12 months), complete reversibility of the signal quenched by oxygen and a quick response time to various oxygen concentrations (<2 s changing from 10 vol% pO2 to 90 vol% pO2). Thus, it is an interesting and promising complex for developing oxygen-selective sensors for gas analysis and the analysis of dissolved oxygen.
•A MIP for extracting Folic Acid (FA) from food extracts has been developed.•The optimum molar ratio was 1:25:250 FA- VBTMAC-EGDMA.•Developed MIP shows high affinity (<2.5 mmol/g) and high imprinting ...factor (>37).•It has been used for developing a dispersive solid-phase extraction protocol.•It exhibits good recovery (≥79.50%) and repeatability (≤13.41 (%RDS)).
This work shows the development of a molecularly imprinted polymer to determine folic acid (FA) in food extracts by using dispersive solid-phase extraction and liquid chromatography coupled to mass spectrometry (LC–MS). Herewith, combinations of monomers (methacrylic acid (MAA), 4-vinylpyridine (4VPy) and vinylbenzyl trimethylammonium chloride (VBTMAC)) and crosslinkers (ethylene glycol dimethacrylate (EGDMA) and divinyl benzene (DVB)) were tested in appropriate solvents. Isotherm tests revealed that the MIP with the highest affinity was obtained by combining VBTMAC and EGDMA. Having checked the appropriate template-monomer-crosslinker ratio, the FA MIP was analyzed for its kinetic and equilibrium binding properties, proving very high affinity (more than 2.5 mmol g−1) and MIP/NIP ratio (up to 37). The FA MIP was used to selectively isolate the compound of interest from lettuce and cookies matrices using a dispersive solid-phase extraction protocol (which exhibited appropriate recovery and repeatability, ≥79.50% and ≤13.41 (%RSD in terms of area values), respectively, as well as absence of matrix effect); the resulting extracts were analyzed by a rapid and reliable LC–MS method.
In the present work a chemometric-assisted molecularly imprinted polymer (MIP)-fluorescence optosensing system has been developed for determining monoamines naphthalene compounds in drinking waters. ...The use of chemometrics for processing flow injection analysis with MIP fluorescence optosensor data allowed the simultaneous determination of the principal monoamine naphthalene compounds 1-naphthylamine (1-NA) and 2-naphthylamine (2-NA) even in presence of potential interferent 1-naphthalenemethylamine (1-NMA). Classical chemometrics tools such as partial least-squares (PLS-1), as well as second-order algorithms like multiway PLS (N-PLS) and unfolded PLS (U-PLS), were successfully applied, assisting fluorescence emission spectra at a fixed excitation wavelength or excitation-emission fluorescence matrices (EEM), respectively, when interferents are considered in the calibration set. The combinations of both N-PLS and U-PLS with residual bilinearization (RBL), achieving the second-order advantage, were satisfactory applied for the simultaneous determination of the main monoamine naphthalene compounds in drinking water, in the presence of a potential interferent without sample pretreatment, even when the later is not modeled in calibration set. Predictive ability, accuracy, figures of merit, as well as advantages and disadvantages of the different strategies were discussed.
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