MIPs-graphene nanoplatelets-MWCNTs modified glassy carbon electrode for the determination of cardiac troponin I.

An electrochemical sensor with high selectivity in addition to sensitivity was developed for the determination of cardiac troponin I (cTnI), based on the modification of cTnI imprinted polymer film on a glassy carbon electrode (GCE). The sensor was fabricated by layer-by-layer assembled graphene nanoplatelets (GS), multiwalled carbon nanotubes (MWCNTs), chitosan (CS), glutaraldehyde (GA) composites, which can increase the electronic transfer rate and the active surface area to capture a larger number of antigenic proteins. MWCNTs/GS based imprinted polymers (MIPs/MWCNTs/GS) were synthesized by means of methacrylic acid (MAA) as the monomer, ethylene glycol dimethacrylate (EGDMA) as the cross linker α,α'-azobisisobutyronitrile (AIBN) as the initiator and cTnI as the template. In comparison with conventional methods, the proposed electrochemical sensor is highly sensitive for cTnI, providing a better linear response range from 0.005 to 60 ng cm-3 and a lower limit of detection (LOD) of 0.0008 ng cm-3 under optimal experimental conditions. In addition, the electrochemical sensor exhibited good specificity, acceptable reproducibility and stability. Moreover, satisfactory results were obtained in real human serum samples, indicating that the developed method has the potential to find application in clinical detection of cTnI as an alternative approach.

[The Properties of an Infrared Hybrid Single Beam Spectrum].

A hybrid single beam spectrum ø(α)=αø(b1)+(1-α)ø(b2)=αø0e(-Kb1)+(1-α)ø0e(-Kb2) is introduced as the combination of two single beam spectra ø(b1) and ø(b2) from the same sample but with different pathlengths (b(1) and b(2)), where α(0＜α＜1) is the hybrid coefficient. The intensity of hybrid spectrum ø(α) can be controlled easily to the desired point by simply choosing an appropriate α. The experimental results showed that hybrid spectrum ø(α) is very nearly identical to ø(b)=ø(0)e-K(b(2)-αb(2)+αb(b)) under appropriate conditions, namely ø(α)≈ø(b) , where ø(b) is the single beam spectrum of the real sample with the pathlength of b(2)-αb(2)+αb(1). Therefore, the desired single beam spectrum ø(b) can be obtained easily by choosing α and we no longer need to prepare IR sample with the thickness of b. Hybrid spectrum method shows valuable potential in application of eliminating background interference.

[Study on the Measurement of Infrared Spectrum for Discontinuous Sample].

The samples to be measured with infrared instrument are usually required to be homogeneous. However, discontinuous sample is quite common in the real infrared measurements, such as, high viscosity liquids containing air bubbles. In this paper, the spectral distortion of discontinuous sample was analyzed with simple theoretical simulation and experimental examples quantitatively. The spectral properties of the discontinuous sample were studied and discussed systematically. Both theoretical computation and experimental results demonstrated that the infrared spectrum of a discontinuous sample was highly similar to that of the uniform sample if suitable experimental conditions were adopted. Our results showed that if infrared samples can be prepared to be thin enough, the infrared spectrum of the discontinuous sample can fulfill the requirement of analysis work nearly perfectly.

Native Defect Luminescence of Zinc Oxide Films and Its Potential Application as White Light Sources.

ZnO light-emitting diodes (LEDs) have an enormous potential in lighting applications. The major issue to be resolved is the generating and control of light emissions. This issue arises from the variation and combination in LED wavelength. We found that defect luminescence of ZnO has a varied wide range of wavelength, which suits to an application of LED for white-light generation. We have shown both experimentally and theoretically that defect emission can be used in ZnO systems. This type of defect has the advantage of not requiring extensive and costly factory systems comparing with traditional doped materials and others. We not only propose potential application of native defect luminescence of Zinc Oxide film for white LEDs-flat light sources, but also have some methods to control defect origins, a certain center position and broad range of the emission band of ZnO film in the initial stage. According to different preparing method and certain experiment conditions, variant white such as whitish and bluish-white etc., primary and important colors- blue bands (455, 458 nm), green bands (517, 548 nm), red bands (613, 569 nm) are obtained respectively. This proved that it is a better road to one white light LED with one kind of material -ZnO.

[How to Remove Water Absorption Bands Completely from IR Spectra of Aqueous Solution].

Infrared spectral studies of aqueous solution have been severely limited by the strong water absorption. Usually, it is very difficult to experimentally achieve perfect compensation between the amount of water that contributes to the sample and background spectra. In the present paper, we introduced a new method to make the infrared bands of water disappear during the measurement of an infrared spectrum for aqueous solution. Both background spectrum of the empty ATR cell and that of the water on ATR cell are used in sequence. Qualified infrared spectra of 10% K2CO3 and 10% BSA aqueous solutions were successfully obtained by ATR accessory (single-reflection) without water interference. The experimental results demonstrated that the new method is fast, effective and powerful. The limitation of the new method is also discussed.

A Method to Obtain a Good Infrared Spectrum of the Wet Acetone Gas Sample without Any Drying Pretreatment.

Water vapor in the beam of a Fourier transform infrared (FTIR) spectrometer or/and in a gas cell is a major source of interference in the infrared measurement of a gas sample. In general, in order to eliminate the effect of water vapor, we have to completely remove these molecules before the measurement of any spectrum. Herein, we provide an approach to collect an IR spectrum of a gas (wet acetone) sample free from water vapor interference without any drying pretreatment. After dozens of scans, the air atmosphere in the sample compartment of the FTIR spectrometer will be slightly adjusted by small amounts of dry air or wet air (room air) depending on the property of water vapor lines (absorbance >0 or absorbance <0). Water vapor lines will then gradually disappear when the ensuing collection process is continued. The experiment results demonstrated that this method is a facile and very effective way to remove water vapor interference. Moreover, this method works still well for the measurement at 0.5 cm(-1) resolution, typically used in the gas infrared measurement.

Combined IR/NIR and density functional theory calculations analysis of the solvent effects on frequencies and intensities of the fundamental and overtones of the C ═ O stretching vibrations of acetone and 2-hexanone.

Vibrational overtone studies primarily focus on X-H stretching overtone transitions, where X is an atom like C, O, N, or S. In contrast, the studies on the C ═ O stretching overtones are very scattered. To advance the research in this field, we measured the fundamental, first, and second overtones of the C ═ O stretching vibration of acetone and 2-hexanone in n-hexane, CCl4, and CHCl3, as well as in the vapor phase using FT-IR/FT-NIR spectroscopy. Density functional theory (DFT) calculations have also been performed to help the assignment of the C ═ O stretching bands and to guide interpretation of the experimental results. It was found that the wavenumbers, absorption intensities, and oscillator strengths of the C ═ O stretching bands show marked solvent dependence. In the fundamental and the first overtone regions, the intensities of the C ═ O stretching vibration were found to be pronouncedly more intense than those of the C-H stretching vibration. In the second overtone region, the intensities of the C-H stretching vibration are comparable to those of the C ═ O stretching vibration. The theoretical and observed decrease in integrated intensity upon going from the fundamental to the first overtone of the C ═ O stretching vibration is around 50, which is significantly larger than those of the O-H, C-H, and S-H stretching vibration. Both the calculated and experimental results suggest that excessive weakness in the C ═ O stretching overtone was shown to be a result of both a low anharmonicity and a substantial reduction in the oscillator strength. These results provide new insight into our understanding of the C ═ O stretching vibration.

[Anomalous absorption and a qualified far infrared spectrum].

The ideal 100% line could not be obtained when the content of water vapor in the spectrometer is constant but high during the whole procedure of a far-infrared spectrum collection. This result indicates that anomalous absorption phenomenon takes place in high relative humidity atmosphere. In the present paper, the influences of the relative humidity of ambient air and spectral resolution on anomalous absorption were studied. It was found that both decreasing the water vapor content in the spectrometer and adopting low spectral resolution are effective methods to avoid anomalous absorption. Furthermore, the water vapor bands can be eliminated by "dry air and wet air titration" in the fluctuant humidity. This provides us a quick and economic method to obtain a qualified far infrared spectrum conveniently. It should be noticed that the working condition for "dry air and wet air titration" is low relative humidity to prevent water vapor abnormal absorption.

[Absorbance of infrared bands and anomalous absorption].

To remove the background signals from an IR spectrum is very useful and ideally all that remain in an IR spectrum are the desired absorption bands. Unfortunately, the removal of background bands is not always completely effective. In the present paper, an absorbance spectrum was obtained by scanning the same sample (polystyrene film or stearic acid KBr disc) both in background and sample single-beam measurements. It was found that a series of residual spikes appear in the strong absorption regions. The residuals are significantly different from that of random noise. There should be a nearly straight line according to theory analysis while spikes appear. Therefore those spikes are called anomalous absorption The experimental results indicate that anomalous absorption is related to the absorbance of infrared bands. If the absorbance of an infrared band is lower than 1.0, anomalous absorption can be suppressed thoroughly. In addition, absorption anomalies can be substantially reduced by reducing the spectral resolution of the spectrum. The reasons for anomalous absorption were discussed and how to prevent the appearance of anomalous absorption by selecting appropriate background samples were suggested.

Infrared band assignments and structure of even-numbered 2-alkyl-7,7, 8, 8-tetracyanoquinodimethane in cast films--two components of the CH2 scissoring vibrations not related to crystal field splitting.

Infrared (IR) spectra were measured for 2-octyl-, 2-dodecyl-, and 2-octadecyl-7, 7, 8, 8-tetracyanoquinodimethane (C8TCNQ, C12 TCNQ and C18 TCNQ) in cast films, and it was found that each spectrum shows two components for the CH2 scissoring band at 1 471 and 1 462 cm(-1). Polarized IR measurements showed that the micro-crystallites in the cast films take a random orientation in the plane of the plate. The intensity ratio of the two bands at 1 471 and 1 462 cm(-1) (I1 471/I1 462) decreases observably with the increase in the length of the alkyl chain. Moreover, the relative intensity of the 1 471 cm(-1) CH2 band to a band at 1 529 cm(-1) (C=C stretching mode of the TCNQ chromophore ring) does not change significantly for the three kinds of C(n) TCNQ while the relative intensity of the 1 462 cm(-1) CH2 band to the band at 1 529 cm(-1) increases markedly with the length of the alkyl chain. The above variations of the CH2 scissoring doublet of C(n) TCNQ are quite different from those of long-chain fatty acids (stearic acid and lignoceric acid) where the splitting of the CH2 scissoring vibration occurs due to a crystal field splitting. Considering the crystal structure of C12 TCNQ and the above spectral variations, the authors assign the two components of the CH2 scissoring bands at 1 462 and 1 471 cm(-1) of the C(n) TCNQ cast films to the interdigitated and non-interdigitated parts of the alkyl chains, respectively. Furthermore, the conclusion that the length of the non-interdigitated part of the alkyl chain is almost unchanged in the three kinds of even-numbered C(n) TCNQ could also be reached.

[Preparation and structural characterization of mixed LB films of TMB * TCNQ and stearic acid].

Mixed LB films of the CT complex of TMB * TCNQ and stearic acid (SA) were prepared. The structures, molecular orientation and morphology of the mixed LB films were characterized by IR, UV-Vis-NIR, XRD and AFM. Our results show that TMB * TCNQ could be deposited on solid substrates by mixing with SA. The complex is mixed-stack, and the degree of charge transfer is 0.35. The chromophore planes of both TCNQ and TMB are perpendicular to the substrate surface and the hydrocarbon chain of SA is inclined at an angle with respect to the substrate surface. There are two kinds of diffraction bands in the XRD spectra, and they probably arise from SA and TMB * TCNQ, respectively. The morphology of mono- and multilayer mixed LB films with molar ratio 1 : 1 consists of many nanorods and particles, and the amount of nanorods and particles increase with increasing the number of monolayers.

A method to collect an infrared spectrum in solution.

Herein we report a new method to collect a qualified infrared spectrum of a solute in solution by two solvent cells with different thickness during background single-beam spectrum scanning. By collecting the background spectrum with two cells (two stages), we successfully achieved accurate solvent compensation between a sample and a reference, namely, the solvent amounts in the sample and background measurements could become congruent. Therefore, the solvent bands were thoroughly suppressed in the infrared spectrum and a qualified spectrum of the solute was obtained.

A multi-walled carbon nanotubes based molecularly imprinted polymers electrochemical sensor for the sensitive determination of HIV-p24.

To develop a rapid, simple and sensitive method for the determination of human immunodeficiency virus p24 (HIV-p24), a novel molecularly imprinted polymers (MIPs) electrochemical sensor was constructed on the surface of a multi-walled carbon nanotubes (MWCNTs) modified glassy carbon electrode (GCE) by surface polymerization using acrylamide (AAM) as functional monomer, N,N'-methylenebisacrylamide (MBA) as cross-linking agent and ammonium persulphate (APS) as initiator. Each modification step was carefully examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscope (SEM). The proposed MIPs electrochemical biosensor exhibited specific recognition to HIV-p24 and displayed a broad linear detection range from 1.0×10-4 to 2ngcm-3 with a low detection limit of 0.083pgcm-3 (S/N=3). This performance is superior to most HIV-p24 sensors based on other methods. Meanwhile, this sensor possessed of good selectivity, repeatability, reproducibility, stability and was successfully applied for the determination of HIV-p24 in real human serum samples, giving satisfactory results. The accuracy and reliability of the sensor is further confirmed by enzyme-linked immunosorbent assay (ELISA).

Catalytic properties of silica/silver nanocomposites.

The catalytic properties of silver nanoparticles supported on silica and the relation between catalytic activity of silver particles and the support (silica) size are investigated in the present article. The silver nanoparticles with 4 nm diameters were synthesized and were attached to silica spheres with sizes of 40, 78, 105 nm, respectively. The reduction of Rhodamine 6G (R6G) by NaBH4 was designed by using the SiO2/Ag core-shell nanocomposites as catalysts. The experimental results demonstrated that the catalytic activity of silica/silver nanoparticles depends on not only the concentration of catalysts (silver) but also the support silica size. Silver particles supported on small SiO2 spheres (approximately 40 nm) show high catalytic activity. Moreover, by making a comparison between the UV-vis spectra of the catalyst before and after the catalytic reaction, we found that the position of surface plasma resonance (SPR) peak of Ag nanoparticles changes little. The above results suggested that the size and morphology of silver particles were probably kept unchanged after the reduction of R6G and also implied that the catalytic activity of silver particles was hardly lost during the catalytic reaction.

[A comparative study on the resolution of second derivative and Fourier self-deconvolution].

Infrared spectra of 2-alkyl-7,7,8,8-tetracyanoquinodimethane (C12H25 TCNQ, C15H31 TCNQ, C18H37 TCNQ) were measured with the resolution of 1 and 4 cm(-1). In order to identify the peak number correctly in the CH2 stretching region, second derivative and Fourier self-deconvolution were applied to the infrared spectra, respectively. The overlapping bands in the CH2 stretching region could be identified when the infrared spectra, which were measured with the resolution of 4 cm(-1), were dealt with by Fourier self-deconvolution. However, the bands overlapped in the CH2 symmetric stretching region could not be observed when these infrared spectra were dealt with by second derivative. The above results reveal that Fourier self-deconvolution method is more powerful than second derivative in identifying bands that are involved in an overlapping band feature.

Concept and properties of an infrared hybrid single-beam spectrum and its application to eliminate solvent bands and other background interferences.

For infrared (IR) spectral measurements, if a quality single-beam background spectrum with desired intensity could be obtained, the contributions from solvent and other background components could be completely suppressed and their bands would not appear in a final transmittance/absorbance spectrum. In order to achieve this ideal but difficult goal, the concept of hybrid single-beam spectrum is introduced in this paper. The hybrid single-beam spectrum (φ h) is defined as a mixture of two single-beam spectra (φ b1 and φ b2) of the same sample but with different pathlengths (b1 and b2), namely, φ h = αφ b1+(1-α)φ b2, where α (0 ≤ α ≤ 1) is the component factor. The properties of the hybrid spectrum have been investigated. Under conditions of b2 > b1 ≥ 0.7 b2 and A max ≤ 0.60 (Amax is the maximum absorbance of b2 sample in the spectral range of interest), all the synthesized hybrid spectra are free from significant distortion regardless of the component factor. Therefore, the hybrid single-beam spectrum with desired intensity can be easily obtained simply by choosing an appropriate component factor. The proposed methodology has been demonstrated experimentally by the complete removal of the interference from the atmospheric water vapor and solvent.

A new method to obtain Fourier transform infrared spectra free from water vapor disturbance.

Infrared absorption bands due to water vapor in the mid-infrared regions often obscure important spectral features of the sample. Here, we provide a novel method to collect a qualified infrared spectrum without any water vapor interference. The scanning procedure for a single-beam spectrum of the sample is divided into two stages under an atmosphere with fluctuating humidity. In the first stage, the sample spectrum is measured with approximately the same number of scans as the background. If the absorbance of water vapor in the spectrum is positive (or negative) at the end of the first stage, then the relative humidity in the sample compartment of the spectrometer is changed by a dry (or wet) air blow at the start of the second stage while the measurement of the sample spectrum continues. After the relative humidity changes to a lower (or higher) level than that of the previously collected background spectrum, water vapor peaks will become smaller and smaller with the increase in scanning number during the second stage. When the interfering water lines disappear from the spectrum, the acquisition of a sample spectrum is terminated. In this way, water vapor interference can finally be removed completely.

Systematic synthesis and characterization of single-crystal lanthanide phenylphosphonate nanorods.

Using low-temperature hydrothermal methods, nanoscale lanthanide phenylphosphonates species with different morphologies, namely, nanoparticles and nanorods, have been systematically synthesized. The possible growth mechanism of these nanorods was discussed. X-ray diffraction, transmission electron microscopy, electron diffraction, and photoluminescence spectra were used to characterize these materials. The photoluminescent properties of Eu(O3PC6H5)(HO3PC6H5) and La0.91Eu0.09(O3PC6H5)(HO3PC6H5) nanorods were discussed.