The blood vessel is part of the circulatory system, and systemic circulation provides the blood supply to all tissues. Arteries are pathways through which the blood is carried, and the capillaries have a key role in material exchange to maintain the tissue environment. Blood vessels have structures appropriate for their functions, and their sizes and cell types are different. In this review, we introduced recent studies of the microfluidic vascular models. The model structures are classified mainly as poly(dimethylsiloxane) and hydrogel microchannels and self-assembled networks. Basic phenomena and functions were realized in vascular models, including fluid shear stress, cell strain, interstitial flow, endothelial permeation, angiogenesis, and thrombosis. In some models, endothelial cells were co-cultured with smooth muscle cells, pericytes, and fibroblasts in an extracellular matrix. Examples of vascular models involving the brain, lung, liver, kidney, placenta, and cancer were also introduced.
When proteins are attached to microstructures such as a metal mesh device, changes in their optical properties occur. These changes have been characterized based on actual measurements in the infrared region of the spectrum. We have previously theoretically and experimentally demonstrated the optical changes associated with streptavidin. Here, we investigate three types of proteins: avidin, BSA, and lysozyme. The three proteins were adsorbed onto three types of metal mesh devices having different resonant frequencies, and the corresponding spectra were measured in the infrared region. The change in the frequency of the dip point in the spectrum was extracted to quantitatively determine the quantity of protein; these results were correlated with the quantitative measurements obtained by electrophoresis. By examining three types of different proteins, it was verified that a variety of proteins can be measured based on the optical characteristics of metal mesh devices.
Proparacaine, one of the most common local anesthetics to facilitate diagnosis and treatment of eye diseases, was assayed by square wave voltammetry using a paste electrode prepared with carbon nanotubes. In cyclic voltammetric studies, proparacaine has exhibited a single irreversible anodic peak at around + 900 mV vs. Ag/AgCl in pH 6.0 Britton–Robinson buffer solution. It was suggested that the peak had appeared due to the oxidation of the NH2 group on the proparacaine molecule. Prior to the determination of the proparacaine by square wave stripping voltammetry (SWSV) on the fabricated multi-walled carbon nanotube paste electrode (MWCNTPE), the accumulation potential (Eacc), accumulation time (tacc), pulse amplitude (ΔE), step potential (ΔEs) and frequency (f ) parameters were optimized. The peak currents plotted in the range of 0.5 – 12.5 mg/L proparacaine exhibited two linear sections with a detection limit of 0.11 mg/L. The results for the determination of proparacaine on a pharmaceutical local anesthetic (Alcaine®) showed that relative standard deviation (RSD) and relative error (RE) were 4.1 and –2.0%, respectively. Selectivity has also been investigated and results showed recoveries of 5.0 mg/L proparacaine in the presence of 5.0 mg/L dopamine, ascorbic acid and uric acid as 106.9 ± 0.8, 99.9 ± 1.2 and 94.1 ± 0.7, respectively.
A highly sensitive flow-injection (FI) method was developed for the determination of ascorbic acid using chemiluminescence (CL) based detection. This method involved the following processes: (1) reduction of tetrachloroaurate(III) in hydrochloric acid with ascorbic acid; (2) on-line extraction of the residual Au(III) with rhodamine B from the aqueous hydrochloric acid solution into toluene, followed by the separation of the Au(III)-containing organic phase from the aqueous phase through a microporous Teflon membrane in the flow system; and (3) the measurement of CL produced in a flow cell upon mixing of the extract stream of Au(III) in toluene with luminol in the reversed micellar medium of cetyltrimethylammonium chloride–water in 1-hexanol–cyclohexane, which was injected into a CL reagent stream. In this procedure, a reduction in the CL intensity occurred due to the addition of ascorbic acid to the Au(III) solution. The CL signal of Au(III) decreased with increasing concentration of ascorbic acid in the aqueous sample solution. The proposed procedure allowed the indirect quantitative determination of ascorbic acid in the range of 1.0 × 10−12 to 1.0 × 10−7 M with a correlation coefficient of 0.987 and relative standard deviation of 2.1% (n = 6) at 1.0 × 10−9 M. The proposed FI-CL methodology was successfully applied for quantitative determination of ascorbic acid in fruit juices and pharmaceutical samples.
Direct and mediated electron transfer (DET and MET) in enzyme electrodes with a novel flavin adenine dinucleotide-dependent glucose dehydrogenase (FAD-GDH) from fungi are compared for the first time. DET is achieved by placing a single-walled carbon nanotube (CNT) between GDH and a flat gold electrode where the CNT is close to FAD within the distance for DET. MET is induced by using a free electron transfer mediator, potassium hexacyanoferrate, and shuttles electrons from FAD to the gold electrode. Cyclic voltammetry shows that the onset potential for glucose response current in DET is smaller than in MET, and that the distinct redox current peak pairs in MET are observed whereas no peaks are found in DET. The chronoamperometry with respect to a glucose biosensor shows that (i) the response in DET is more rapid than in MET; (ii) the current at more than +0.45V in DET is larger than the current at the current-peak potential in MET; (iii) a DET electrode covers the glucose concentration range for clinical requirements and is not susceptible to interfering agents at +0.45 V; and (iv) a DET electrode with the novel fungal FAD-GDH does not affect sensing accuracy in the presence of up to 5 mM xylose, while it often shows a similar response level to glucose with other conventionally used fungus-derived FAD-GDHs. It is concluded that our DET system overcomes the disadvantage of MET.
Early diagnosis of cancer is the most important factor that increases the success of treatment. Therefore, the development of new diagnostic tools is a necessity. In this study, a new electrode surface was developed via modification of a disposable titanium electrode with anodic oxidation and coating of gold nanoparticle and chitosan. Titanium electrodes were anodized by several anodization parameters to obtain a nanoporous surface and characterized by scanning electron microscopy. Electrodes anodized in optimum conditions were modified with gold nanoparticles and chitosan for enhancing conductivity and functionalizing the surface of electrode, respectively. To detect prostate specific antigen (PSA), anti-PSA was bound onto the functional electrode surface. Modified electrodes were characterized with scanning electron microscopy and cyclic voltammetry and used for chronoamperometric detection of PSA. Limit of detection (LOD) of the designed electrode was found to be 7.8 ng mL−1 for PSA in a linear range of 0 – 100 ng mL−1.
We report on a paper-based 2,2-diphenyl-1-(2,4,6-trinitrophenyl)hydrazyl (DPPH) assay for a simple, inexpensive, low reagent and sample consumption and high throughput analysis of antioxidant activity. The paper-based device was fabricated using a lamination method to create a 5-mm in diameter circular test zone that was embedded with a DPPH reagent. The analysis was carried out in one-step by dropping an antioxidant/sample onto the test zone. After reduction by the antioxidant, the DPPH radicals become stable DPPH molecules, resulting in a change in color from deep violet to pale yellow. The violet color intensity of DPPH was inversely proportional to the antioxidant activity of the samples, and was measured using imaging software. A high precision and a low limit of detection were found in the analysis of six standard antioxidants including gallic acid, trolox, ascorbic acid, caffeic acid, vanilliic acid and quercetin. The device was then validated against the traditional spectrophotometric DPPH assay by analyzing the antioxidant activity of 7 tea samples. The results showed no significant difference for gallic acid equivalent for all 7 samples obtained from the two methods at the 95% confidence level, indicating that the developed method was reliable for antioxidant activity analysis of real samples. Finally, the paper-based DPPH device was found to be stable over 10 days when stored in a refrigerator (2 – 4°C), making it an easy-to-use device for end-users.
A new and simple method for the simultaneous determination of cations and anions by microchip electrophoresis with capacitively coupled contactless conductivity detection (ME-C4D) is described. The best analytical performance was found by applying a sinusoidal wave with 800 kHz frequency and 20 Vpp amplitude. An optimized background electrolyte (BGE) composed of 20 mM His/MES and 0.01 mM CTAB was chosen for the simultaneous analysis. Samples containing K+, Na+, and Li+ as the cations and Cl−, F− and PO43− as anions were analyzed simultaneously in a single run (within 3 min). The reproducibility obtained by the method was compared with those obtained in previous studies that had employed simultaneous analysis of anions and cations by ME-C4D. The proposed simultaneous determination method is inexpensive, simple, fast, easy to operate, and offers a high degree of integration.
The effects of the functional group density in the stylene-divinylbenzene copoymer phase and of the supporting electrolyte concentration in the aqueous phase on the perfomance of the iminodiacetate (IDA)-type chelating resin were studied in terms of contribution of an ion-exchange mechanism. High hydrophobicity of the resin having a low functional group density interfered with penetration of aqueous solutions into the resin phase to slow the acid-base reaction and the adsorption reaction. Uptake of the cation in the supporting electrolyte into the resin phase was clearly indicated in each of two acid dissociation reactions. The high concentration of the supporting electrolyte enhanced acid dissociation of the IDA group, and a singly deprotonated species interacting with the supporting electrolyte cation strongly interfered with adsorption by the ion-exchange mechanism, while only slightly interfering with adsorption by the complexation. Both the complexed and ion-exchanged species respectively involving two or more IDA groups were destabilized to reduce the adsorption capacity of the resin having the low functional group density.
Materials which can be combined with riboflavin specifically based on smart functionalized polymer were studied for their ability to selectively extract riboflavin from beer. The extraction was done directly by the affinity interaction of riboflavin with the riboflavin aptamer or riboflavin binding protein (RBP). Poly(N-isopropylacrylamide) (PNIPAAm) was introduced as a carrier and modified with riboflavin aptamer and RBP, respectively, in order to be conducive to the separation of riboflavin originally present in the beer. The produced complexes can be readily separated from the aqueous phase and benefited from the temperature sensitive property of this smart polymer. The study showed riboflavin could be selectively removed from a standard solution and beer satisfactorily and the nonspecific binding was almost negligible. In the manufacturing process of beer, this separation method has a great potential to prolong the storage period of beer and improve the quality of the products.
A new combination between selective polymer monolith microextraction (PMME) and sensitive differential pulse voltammetry (DPV) was developed for the determination of the phytohormone salicylic acid (SA) in Actinidia chinensis. A molecularly imprinted monolithic column (MIMC) thermally in-situ polymerized in a micropipette tip by using SA as a template, 4-vinyl pyridine (4-VP) as a functional monomer and ethylene glycol dimethacrylate (EGDMA) as a cross-linker in the mixed porogen of toluene and dodecanol, was employed for the microextraction of SA. The prepared MIMC was characterized by a Fourier transform infrared spectrometer (FI-TR), scanning electron microscope (SEM) and thermo gravimetric analysis (TGA). The results confirmed the binary continuous structure of the porous network. The extracted SA was determined by DPV on a graphene oxide (GO) modified electrode. The joint conditions between MIMC and DPV were investigated practically. Under the optimum conditions, SA could be determined selectively and sensitively in a linear range from 0.1 to 60.0 μg g−1. The limit of detection was 0.03 μg g−1 and the recoveries were between 86.2 and 105.2%. The proposed joint method was successfully used to determine SA in Actinidia chinensis.
The determination of sulfur in apricot and grape samples was performed by using high-resolution continuum source electrothermal molecular absorption spectrometry based on vaporization of the carbon monosulfide (CS) molecule. CS forms in the gas phase without the addition of any molecule-forming element, since graphite cuvette contains plenty of carbon as well as food samples. A mixture of 15 μg Pd + 10 μg Mg was used in solution as the chemical modifier. The best sensitivity was obtained at 900°C of the pyrolysis temperature with a K2SO4 calibration solution. The calibration plot drew a linear path between 50 and 1600 ng of sulfur, and the limit of detection was found to be 23 ng. The accuracy of the method was confirmed with the use of a standard reference material (Rice Flour, NIST SRM 1568a). The sulfur content in chemically dried apricot samples (1987 ± 45 mg/kg) was determined to be higher than that of apricot samples dried under sunshine.
We investigated melanin radicals in paraffin-embedded malignant melanoma (MM) using a surface-type dielectric resonator for X-band electron paramagnetic resonance (EPR) and analyzed the radical species. The surface-type resonator’s performance was examined using 5 – 10 μL of 0.1 mM 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL) aqueous solution in a 1.0-mm (i.d.) glass capillary as well as 1,1-diphenyl-2-picrylhydrazyl (DPPH) powder. The surface-type detection has approximately two times poorer S/N ratio than commercial insertion-type detection. A sample of the paraffin-embedded MM specimen was used for the radical detection. We obtained an EPR spectrum of melanin radicals in the paraffin-embedded melanoma sample (size ∼3 × 4 × 3 mm). A single line (∼0.64 mT peak-to-peak line-width) with a small shoulder was observed and was identified as a pheomelanin-related radical. The pheomelanin radical can be directly related to the MM. Thus, the present results were a good indication for noninvasive measurement, as well as for detailed analyses of melanin radicals in human MM.
N-Acetylneuraminic acid (NANA) has been reported to react with hydrogen peroxide in vitro to produce 4-(acetylamino)-2,4-dideoxy-D-glycero-D-galacto-octonic acid (ADOA). We labeled NANA and ADOA with 4-(N,N-dimethylaminosulfonyl)-7-piperazino-2,1,3-benzoxadiazole (DBD-PZ) for simultaneous detection. The derivatized NANA and ADOA were separated using hydrophilic interaction liquid chromatography (HILIC) with fluorescence detection. The calibration curves of DBD-PZ-derivatized NANA and ADOA showed good linearity in the range of 221 fmol to 1.5 nmol, and 44 fmol to 1.5 nmol, respectively. This analytical method has high specificity and is useful for the detection of NANA and ADOA in saliva and serum.
We describe further potential of generalized 2D correlation analysis, aiming to realize the automation of the sequential order determination of signal variations. By modeling unimodal waveforms using quadratic functions, we can analytically express 2D correlation functions to yield an index to determine the sequential order. Based on the obtained results, we find an exception for determining the sequential order of signal variations. To resolve the exception, we suggest an extended way of interpreting the sequential order of signal intensity changes.
A method for nickel preconcentration by coprecipitation using Al(OH)3, followed by centrifugation and dissolution with HNO3 prior to a determination by flame atomic absorption spectrometry (FAAS), was investigated. Preconcentration factors of 30 and 200 were tested, and the detection limit (3 × sd/m, n = 10) was 0.05 μg L−1. The method was applied to real samples, and the results agreed with those obtained directly by graphite furnace atomic absorption spectrophotometry.
In this work, we applied post-column reaction gas chromatography (GC) using a flame ionization detector (FID) system to study nitrogen-containing organic compounds (NOCs). The results were subsequently validated. After separation by column, the target components were converted to carbon dioxide using an oxidizing catalyst and then reduced to methane, followed by detection using an FID. SI-traceable testing mixtures containing NOCs (isoprocarb, napropamide, and pendimethalin) were prepared by the gravimetric blending method. These mixtures were analyzed using a post-column reaction GC-FID system; standard materials of hydrocarbons were used as calibrants in this analysis. The determined values were compared with the values obtained for samples prepared at the corresponding concentrations, and statistical analyses were performed in all cases. It was shown that the determined and prepared values agreed well with each other within the uncertainty limits.