Jingsong Li

Applications of absorption spectroscopy using quantum cascade lasers.

Infrared laser absorption spectroscopy (LAS) is a promising modern technique for sensing trace gases with high sensitivity, selectivity, and high time resolution. Mid-infrared quantum cascade lasers, operating in a pulsed or continuous wave mode, have potential as spectroscopic sources because of their narrow linewidths, single mode operation, tunability, high output power, reliability, low power consumption, and compactness. This paper reviews some important developments in modern laser absorption spectroscopy based on the use of quantum cascade laser (QCL) sources. Among the various laser spectroscopic methods, this review is focused on selected absorption spectroscopy applications of QCLs, with particular emphasis on molecular spectroscopy, industrial process control, combustion diagnostics, and medical breath analysis.

Contributed Review: Quantum cascade laser based photoacoustic detection of explosives

Detecting trace explosives and explosive-related compounds has recently become a topic of utmost importance for increasing public security around the world. A wide variety of detection methods and an even wider range of physical chemistry issues are involved in this very challenging area. Optical sensing methods, in particular mid-infrared spectrometry techniques, have a great potential to become a more desirable tools for the detection of explosives. The small size, simplicity, high output power, long-term reliability make external cavity quantum cascade lasers (EC-QCLs) the promising spectroscopic sources for developing analytical instrumentation. This work reviews the current technical progress in EC-QCL-based photoacoustic spectroscopy for explosives detection. The potential for both close-contact and standoff configurations using this technique is completely presented over the course of approximately the last one decade.

Wavelet Transform Based on the Optimal Wavelet Pairs for Tunable Diode Laser Absorption Spectroscopy Signal Processing

This paper presents a novel methodology-based discrete wavelet transform (DWT) and the choice of the optimal wavelet pairs to adaptively process tunable diode laser absorption spectroscopy (TDLAS) spectra for quantitative analysis, such as molecular spectroscopy and trace gas detection. The proposed methodology aims to construct an optimal calibration model for a TDLAS spectrum, regardless of its background structural characteristics, thus facilitating the application of TDLAS as a powerful tool for analytical chemistry. The performance of the proposed method is verified using analysis of both synthetic and observed signals, characterized with different noise levels and baseline drift. In terms of fitting precision and signal-to-noise ratio, both have been improved significantly using the proposed method.

Mid-infrared gas absorption sensor based on a broadband external cavity quantum cascade laser

We developed a laser absorption sensor based on a pulsed, broadband tunable external cavity quantum cascade laser (ECQCL) centered at 1285 cm-1. Unlike traditional infrared spectroscopy system, a quartz crystal tuning fork (QCTF) as a light detector was used for laser signal detection. Fast Fourier transform was applied to extract vibration intensity information of QCTF. The sensor system is successfully tested on nitrous oxide (N2O) spectroscopy measurements and compared with a standard infrared detector. The wide wavelength tunability of ECQCL will allow us to access the fundamental vibrational bands of many chemical agents, which are well-suited for trace explosive, chemical warfare agent, and toxic industrial chemical detection and spectroscopic analysis.

Detection of multiple chemicals based on external cavity quantum cascade laser spectroscopy

A laser spectroscopy system based on a broadband tunable external cavity quantum cascade laser (ECQCL) and a mini quartz crystal tuning fork (QCTF) detector was developed for standoff detection of volatile organic compounds (VOCs). The self-established spectral analysis model based on multiple algorithms for quantitative and qualitative analysis of VOC components (i.e. ethanol and acetone) was detailedly investigated in both closed cell and open path configurations. A good agreement was obtained between the experimentally observed spectra and the standard reference spectra. For open path detection of VOCs, the sensor system was demonstrated at a distance of 30m. The preliminary laboratory results show that standoff detection of VOCs at a distance of over 100m is very promising.

Quantum cascade laser based photoacoustic detection of explosives

H metal ion pollution is a serious environment problem that has attracted more and more attentions in recent years. Mercury ion (Hg2+) and lead ion (Pb2+) are two of the most toxic metallic pollutants even at an extremely low concentration. Copper ion (Cu2+), an essential micronutrient element for human life, can cause adverse health effects when present in high concentrations. Considerable efforts have been devoted to the detection of heavy metal ions due to their high toxicity towards the ecosystem and human health. Unlike the traditional detection technologies, we have developed some simple and sensitive biosensors without the requirement of sophisticated instrumentation and skilled personnel. With the combination of DNAzyme, DNA machine and lateral flow biosensor, the visual instrument-free method offers a point-of-use solution for heavy metal ion analysis and provides a basis for the future work aiming at the development of household devices for sensitive detection of various analytes.Purpose: The aim of our present work was to develop and validate a reverse phase high-performance liquid chromatography (RP-HPLC) method for the determination of Decitabine (DCB). The developed method was further applied to observe the degradation of DCB under various stress conditions. Methods: Chromatographic separation was achieved on C18, 250 × 4.6 mm, particle size 5 μm, Agilent column, using ammonium acetate (0.01M) as mobile phase with flow rate of 1mL/min and injection volume was 20 μL. Quantification was carried out with UV detector at 230 nm with a linear calibration curve in the concentration range of 10–100 μg/mL based on peak area. Thus, developed method was validated for linearity, accuracy, precision, and robustness. Results: Linearity was found to be in the range between 10–100 μg/mL with a significantly higher value of correlation coefficient r = 0.9994. The limits of detection (LOD) and the limits of quantification (LOQ) were found to be 1.92μg/mL and 5.82 μg/mL respectively. Moreover, validated method was applied to study the degradation profile of DCB under various stress degradation conditions. Examination of different stress conditions on degradation of DCB showed that its degradation was highly susceptible to oxidative condition as 31.24% of drug was degraded. In acidic and alkaline conditions, the drug was degraded by 21.03% and 12.16% respectively, while thermal and photolytic condition causes least degradation, i.e. 0.21% and 0.3% respectively. Conclusion: The proposed method was found to be sensitive, specific and was successfully applied for the estimation of DCB in bulk drug, and lipid based nanoparticles.Abstract: A validated stability-indicating HPLC method has been reported for the determination of Ilaprazole in bulk drug and tablet. The drug was subjected to the various stress conditions as per the ICH guidelines. The degradation behavior of Ilaprazole was studied under hydrolytic, oxidative, photolytic and thermal conditions and was found to be unstable in almost all conditions except under alkaline and photolytic conditions. The separation of drug and its degraded products was carried out on Kinetex C-18 100A (5µ, 250×4.6 mm) column. The initial mobile phase composition used was Acetonitrile and water in the ratio 50:70v/v for 1 min then changed to 70:30v/v in next 6 min and finally equilibrated back to initial composition in 14min. The method was applied for the determination of Ilaprazole in marketed tablet formulation. The detection was carried at 305 nm using PDA detector with a flow rate of 1.0ml/min and injection volume 20µl. The validation of developed method was performed for linearity, accuracy, precision, selectivity and specificity and robustness.In the present work orodispersible tablets of Ondansetron hydrochloride were formulated by effervescent and sublimation method using factorial design. In the effervescent method, crospovidone (1.31%-4.68%) was used as superdisintegrant whereas citric acid (7.95%-18.04%) and sodium bicarbonate (5.22%-28.77%) were used as effervescent agent. In the sublimation method, crospovidone (1.58%-4.41%) was used as superdisintegrant whereas camphor (6.34%-17.35%) was used as subliming agent. The prepared batches of tablets were evaluated for hardness, friability, drug content uniformity, wetting time, disintegration time and In Vitro drug release pattern. Total 15 batches were formulated by effervescent method and 9 batches were formulated by sublimation method. Disintegration time of the formulations prepared by effervescent method was found between 13-36 secs whereas formulations prepared by sublimation method showed disintegration time between 7-39 secs. Among all the formulations, the formulation (S6) prepared by sublimation method using crospovidone 4% and camphor 8% was found to have the minimum disintegration time (7 seconds). Finally, it was concluded that Orodispersible tablet of Ondansetron Hydrochloride can be successfully formulated using effervescent and sublimation method and can be used as a novel drug dosage form for pediatric and geriatric with improved patient compliance and enhanced bioavailability.I this presentation, the interaction between cilostazol and two different cyclodextrins (β-CD and DM-β-CD) is studied by using LC. The capacity factors (k) of cilostazol were monitored in the presence of increasing concentrations of β-CD or DM-β-CD from the reduction of the retention time (tR). It was observed that cilostazol forms a 1:1 inclusion complex with β-cyclodextrin (β-CD) and dimethyl-β-cyclodextrin (DM-β-CD) at 250C, 370C and 450C. The interaction of cilostazol with DM-β-CD was more efficient and the highest the formation constant (K) was found for DM-β-CD (23.82M-1) at 250C. Moreover, the values of K decreased as the system temperature increased. To obtain the information on the mechanism of cilostazol affinity for β-CD and DM-β-CD, the thermodynamic parameters of the complexation (ΔG, ΔH, and ΔS) were studied. Finally, a comparison of the K values obtained for the two different cyclodextrins revealed that the K values of the complexation are dependent upon the structure of the host molecule. The change in the thermodynamic parameters suggested that the complexation could proceed spontaneously (ΔG<0) along with the releasing of heat (ΔH<0) and the decrease of entropy (ΔS<0).T light scattering of single nanoparticle, such as gold and silver nanoparticles, is stable and efficient, hence the applications of single nanoparticle-based dark-field microscopic imaging have attracted extensive attention. Both the changes of single nanoparticle scattering imaging color and scattering intensity can be used as effective detection signal in analytical chemistry. In the author’s group, to study the localized surface plasmon resonance (LSPR) light scattering of single nanoparticle, first the shape effect of single silver nanoparticle on the scattering light color and refractive index sensitivities was investigated. It was found that particles with a large radial ratio or a tip structure always had a higher sensitivity which could be due to the LSPR maxima at long wavelengths and the strong electric field intensity distribution. Then single nanoparticle-based RGB analytical method was established by coding the colors of the scattering light of individual nanoparticles with the RGB system, and the imaging date was manipulated with the IPP software. In addition, the scattering light intensity of single gold nanoparticle was digitized and expressed as digital information through the aforementioned software. Based on the RGB system and digitized method, it was established new scattering analytical method which had been certified in our other energy transfer experiment. Furthermore, the single nanoparticle-based dark-field microscopic imaging was also used to monitoring some chemical reactions. Real-time monitoring of the etching process of gold nanoparticles by iodine, in situ growth of single Ag@Hg nanoalloys and photochemical reaction were successfully achieved by dark-field microscopic imaging. In addition to the chemical reactions, the single nanoparticle-based dark-field microscopic imaging has a potential to real-time monitoring the intracellular biochemical reactions and infection process of bacteria and virus which may provide a new method for the diagnosis of the disease.

Site-selective nitrogen isotopic ratio measurement of nitrous oxide using a TE-cooled CW-RT-QCL based spectrometer

The feasibility of laser spectroscopic isotopic composition measurements of atmospheric N2O was demonstrated, although making them useful will require further improvements. The system relies on a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser source emitting wavelength of around 4.6μm, where strong fundamental absorption bands occur for the considered specie and its isotopomers. The analysis technique is based on wavelength modulation spectroscopy with second-harmonic detection and the combination of long-path absorption cell. Primary laboratory tests have been performed to estimate the achievable detection limits and the signal reproducibility levels in view of possible measurements of (15)N/(14)N and (18)O/(16)O isotope ratios. The experiment results showed that the site-selective (15)N/(14)N ratio can be measured with a precision of 3‰ with 90s averaging time using natural-abundance N2O sample of 12.7ppm.

Quantum cascade laser based absorption spectroscopy for direct monitoring of atmospheric N2O isotopes

A compact high-resolution spectroscopic sensor using a thermoelectrically (TE) cooled continuous-wave (CW) room temperature (RT) quantum cascade laser (QCL) operating at 4.6u202fμm, is employed for simultaneous detection of three main isotopic species (14N15N16O, 15N14N16O and 14N14N16O). To enable a high-precision analysis of N2O isotopic species at ambient mixing ratios, a liquid nitrogen-free preconcentration unit is built to trap and load atmospheric N2O. The absorption spectra of 14N15N16O, 15N14N16O, and 14N14N16O between 2188.6u202fcm-1 and 2189u202fcm-1 are measured, and the respective ratios of the rare to the abundant isotopologues abundances are demonstrated. Moreover, spectroscopic parameters of pressure-broadening coefficient for selected absorption lines have been determined, and a good agreement is obtained by comparing with HITRAN database.

Measurements of new absorption lines of acetylene at 1.53 μm using a tunable diode laser absorption spectrometer

A new investigation of acetylene absorption lines between 6526.5 and 6531.5cm-1 spectral region was performed by using a long-path absorption cell based tunable diode laser absorption spectrometer. The multi-spectrum fitting procedure has been applied to these intensive absorption lines of acetylene within the spectral range of particular interest to recover the line parameters. Line intensities and line positions of total 42 lines of acetylene were reported, including 22 new lines precisely identified for the first time. The reported results will be valuable to complete the spectroscopic databases of acetylene, and also be useful for upgrading our newly developed TDLAS sensor system for industrial C2H2 gas detection.

Recent progress on gas sensor based on quantum cascade lasers and hollow fiber waveguides

Mid-infrared laser spectroscopy provides an ideal platform for trace gas sensing applications. Despite this potential, early MIR sensing applications were limited due to the size of the involved optical components, e.g. light sources and sample cells. A potential solution to this demand is the integration of hollow fiber waveguide with novelty quantum cascade lasers.Recently QCLs had great improvements in power, efficiency and wavelength range, which made the miniaturized platforms for gas sensing maintaining or even enhancing the achievable sensitivity conceivable. So that the miniaturization of QCLs and HWGs can be evolved into a mini sensor, which may be tailored to a variety of real-time and in situ applications ranging from environmental monitoring to workplace safety surveillance. In this article, we introduce QCLs and HWGs, display the applications of HWG based on QCL gas sensing and discuss future strategies for hollow fiber coupled quantum cascade laser gas sensor technology.