Terahertz absorption characteristics of strong acid solution based on microfluidic chip

Because the vibrational and rotational energy levels of many biomolecules are in the terahertz range, they can interact with terahertz. In addition, the photon energy of terahertz wave is very low, only meV level, which will not cause damage to the material, so terahertz technology can be used for non-destructive detection of biological molecules. As we all know, many biomolecules need to maintain their biological activity in aqueous solution, so it is of practical significance to study the biological characteristics in aqueous solution. The combination of terahertz and microfluidic technology can greatly reduce the absorption of liquid samples to terahertz, so it can detect more accurate signals. Therefore, terahertz time domain spectroscopy technology has a good application prospect in biological detection. The terahertz transmission characteristics of different sodium salts standing in electric field for different time are studied. Double layer terahertz microfluidic chips were prepared by using cycloolefin copolymer (COC) materials with high transmission rate for terahertz wave. The terahertz transmission characteristics of four kinds of sodium salts under the action of electric field were tested by using microfluidic chips with strong sealing performance. In order to avoid the influence of ionic impurities in aqueous solution, deionized water was used to prepare the solution. NaCl, CH₃COONa, NaHCO₃ and Na₂CO₃ electrolyte solutions with concentration of 0.9 mol/L are selected. The four solutions were injected into the microfluidic chip in turn, and then put into the external electric field device. The electric field treatment time is 0 min, 5 min, 10 min, 15 min and 20 min respectively. The transmission intensity is measured by terahertz time domain spectroscopy system every five minutes, and the corresponding spectrum can be obtained. The results show that with the increase of electric field time, the THz transmission intensity of the four sodium salt solutions increases.

Metamaterials, artificial electromagnetic media consisting of periodical subwavelength metal-based micro-structures, were widely suggested for the absorption of terahertz (THz) waves. However, they have been suffered from the absorption of THz waves just in the single-frequency owing to its resonance features. Here, in this paper, we propose a simple periodical structure, composed of two 90 degree crossed dumbbell-shaped doped-silicon grating arrays, to demonstrate broadband THz wave absorption. Our theoretical and experimental results illustrate that THz waves can be efficiently absorbed more than 95% ranging from 0.92 THz to 2.4 THz. Such an ultra-wideband polarization-independent THz absorber is realized mainly based on the mechanisms of the anti-reflection effect together with the [±1, 0]-order and [0, ±1]-order grating diffractions. The application of our investigation can be extend to THz couplers, filters, imaging, and so on.

Summary form only given. The polarization pulse shaping, that is, the manipulation of the direction and timing of electromagnetic fields, has played a pivotal role in handling the interactions between strong pulsed light fields and matter, such as in increasing multiphoton ionization yield, optical gating for higher harmonic generation, and photoassisted asymmetric synthesis of chiral molecules. Recent advances in terahertz technologies have extended the scope of these studies to terahertz frequency ranges. The shaping of the temporal trajectories of terahertz vector fields could substantially increase the degree of freedom of such nonlinear interactions. However, to date, the methods for terahertz polarization pulse shaping have been limited to combining terahertz waves generated by multiple laser pulses, and their flexibility is far behind the Fourier-synthesis based shaping techniques available for optical frequencies which can actively control numerous parameters necessary to generate tailored pulses.In this paper, we experimentally demonstrate the generation of arbitrary terahertz vector waveforms via conversion from polarization-shaped laser pulses designed on the basis of the polarization selection rules for optical rectification in a threefold crystal. The terahertz electric field generated through the optical rectification process is described as a linear response to the intensity envelope of the fundamental laser pulse, which is well described by the instantaneous Stokes parameters (ISPs), Si(t) (i = 0 to 3) [1]. When the light propagates along a threefold axis of a nonlinear optical crystal, the polarization selection rule for the optical rectification becomes very simple [2]. For example, when the excitation laser pulse propagates along a threefold [111] axis of GaP, the generated terahertz is described as follows: ETHz ] ∞ x (t) = ETHz y (t) 0 S1(τ) ] α(t - τ) -S2(τ) dτ. The coordinates are taken as x II [110], y II [112], z II [111] in GaP. The function α(t) is the impulsive response determined by the strength of second-order nonlinear response, absorption of terahertz waves by the crystal, and phase matching conditions. According to Eq. (1), one can generate terahertz waves with arbitrary Ex(t) and Ey(t), if S1(t) and S2(t) can be tuned arbitrarily. For this purpose, we build a Fourier-synthesis based optical pulse shaper with a liquid-crystal spatial light modulator [3]. This pulse shaper can modulate the phases of the two cross linearly polarized components for each frequency. We developed an explicit method to design these phases required to achieve desired S1(t) and S2(t) by this pulse shaper. For example, Fig. 1 shows an experimentally obtained electric field trajectory of a circularly polarized terahertz pulse. To achieve this, we rotated the trajectory of [S1(t),S2(t)] vector in the (S1,S2) plane, which means that the polarization azimuth of the incident laser rotates in time. Owing to the direct design of the parameters of the pulse shaper, we have achieved to control not only just the polarization state of the terahertz pulse, but also other various parameters such as its central frequency, bandwidth, and spectral phases.

We have demonstrated a light control terahertz modulation system based on the semiconductor material, the system is composed of a commercial 850nm 10Gbps light source and a continuous THz source. The semiconductor device is the epitaxial growth Si layer on Si substrate wafer. When the 850nm light and continuous terahertz waves incident simultaneously to this semiconductor wafer, the modulated light can excite photogenerated carriers. And the carrier determines the absorption of terahertz waves, so the amplitude of output terahertz waves will be modulated. The tested modulation depth is 35%. The semiconductor material carriers lifetime determines both the modulation depth and modulation speed. So the carrier lifetime should be trade off considered. The modulation speed has been theoretical calculated and experimental tested. The carriers lifetime is tested about 2ns, and the modulation speed is calculated beyond gigabit per second.

Two-color laser mixing in gases can result in the emission of broadband, single-cycle terahertz (THz) pulses. In this study, we find that THz wave absorption is observed when the THz wave and preplasma beam are focused on the same point, and that the wavelength of the preplasma beam can influence the absorption. The experimental results reveal that the THz wave absorption becomes less pronounced with increasing preplasma wavelength. We found that the absorption decreased sharply at a wavelength of 1400 nm, which may be related to the preplasma density, and the preplasma fluorescence profiles were measured using a charge-coupled device arrangement to prove our conjecture. In addition, the full-width at half-maximum of the frequency of the THz wave becomes broadened during absorption. The experimental results agree well with our presented model.

Research on microfluidic devices for biological analysis has progressed sufficiently to be developed into point-of-care diagnostics products. The goal of this thesis is to improve multiple aspects of capillary-driven microfluidic devices. In particular, the objective is to provide devices with a fast time to result, that are simple to use (one-step), that can be portable, that accept a variety of samples, that operate reliably, that provide a range of detection signals, that are mass manufacturable at lost cost, and that are able to detect medically relevant biological molecules. First, we survey the evolution of microfluidic research into portable medical diagnostic devices. By looking at several gaps and opportunities in current medical diagnostics, we provide an overview of research topics that have the potential to shape the next generation of point-of-care diagnostics. Specifically we explain technologies in the order of sample interacting with different components of a device. We investigate the materials, surface treatments, sample processing, microfluidic elements (such as valves, pumps and mixers), receptors and analytes and the integration of these components into a device that might conceivably leave the laboratory for the hands of consumers. The knowledge of what is important in a point-of-care diagnostics device was used to develop a proof of concept. One of the main challenges is to make microfluidics easy to use by incorporating reagents and microfluidic elements. We integrated a number of functional elements on a chip such as a sample collector, delay valves, flow resistors, a deposition zone for detection antibodies (dAbs), a reaction chamber sealed with a polydimethylsiloxane (PDMS) substrate, and a capillary pump and vents. We further incorporated capture antibodies (cAbs), detection antibodies (dAbs) and analyte molecules for making one-step immunoassays. The integrated microfluidic chip requires only the addition of sample to trigger a sequence of events controlled by capillary forces to detect C-reactive protein (CRP), a general inflammation and cardiac marker, at a concentration of 1 ng mL-1 within 14 min using only 5 µL of human serum. The proof-of-concept is extended to easily modify several assay parameters such as the flow rates and the volumes of samples for tests, and the type of reagents and receptors for analytes. The multiparametric microfluidic chip is capable of analyzing 20 µL of human serum in 6 parallel flow paths in a range of flow rates with filling times from 10 minutes to 72 minutes. The asymmetric release of dAbs in a stream of human serum is compensated by a Dean flow mixer. Sample is equally split into 6 reaction chambers connected to flow resistances that vary flow rates, and the kinetics of capture of analyte-dAb complexes. The increased incubation time leads to a fourfold increase in detection signal in the reaction chamber with the longer incubation time. Furthermore, integrating reagents and controlling their release is essential for simple and accurate point-of-care diagnostic devices. We developed reagent integrators (RIs) to release small amounts of dried reagents (ng quantities and less) into microliters of sample. Typical RIs are composed of an inlet splitting into a central reagent channel, with a high hydraulic resistance, and two diluter channels. Reagents spotted in the central channel reconstitute in sample during filling and merge at the end of the RI with a dilution factor corresponding to the relative hydraulic resistance of the channels forming the RI. RIs are simple to integrate in lateral flow assays and provide a great degree of control over reagent integration and dissolution. Finally, the one-step capillary-driven microfluidic chips have the ability to not only detect a variety of proteins, but also to detect nucleic acids for molecular diagnostics. These devices, especially if manufactured in low cost plastic and used with portable fluorescence readers, have the potential to identify a wide variety of health conditions and to enable truly decentralized medical diagnostics.

The application of the fractional calculus model for dispersion and absorption in dielectrics I. Terahertz waves

Terahertz wave absorption via preformed air plasma

Application of terahertz time-domain spectroscopy and chemometrics-based crested porcupine algorithm in identification of different medicinal parts of Angelica sinensis

Norfloxacin is a kind of quinolone bactericide which is widely used in food industry, livestock feed and medicine area. At present, how to develop a rapid, convenient and accurate technique for qualitative and quantitative detection of norfloxacin is still a challenge. In this study, Terahertz Time-domain Spectroscopy technology (THz-TDS) was used to explore qualitative and quantitative analysis of norfloxacin. Forty-five norfloxacin samples with different levels were prepared. The pure norfloxacin powder was mixed with polyethylene (PE) powder together and made into tablets by tablet-making machine. The minimum detection concentration was 10% and the maximum detection concentration evaluated in the paper was 90%. Then, terahertz (THz) spectra of each sample were measured on K15 THz-TDS equipment. The multiple linear regressions and the partial least squares regression algorithms were used to establish a model to make quantitative analysis. From the results, two typical fingerprint peaks of norfloxacin in terahertz band were observed at 0.944 THz and 1.206 THz, and the correlation coefficient and the root mean square error of the established model reached 0.9908 and 0.0481, respectively, which showed that the model performed well for the prediction. This preliminary study indicates that THz spectroscopy has great potential for future screening applications to detect the presence of norfloxacin residues in food, livestock feed and medicine industries. Keywords: Terahertz spectroscopy, norfloxacin, qualitative and quantitative detection, model, correlation coefficient DOI: 10.25165/j.ijabe.20171005.2962 Citation: Long Y, Li B. Preliminary study on qualitative and quantitative detection of norfloxacin based on terahertz spectroscopy. Int J Agric & Biol Eng, 2017; 10(5): 262–268.

Recently, the classical <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -scan technique is considered feasible for the nonlinear measurement of liquid water in the low-frequency terahertz (THz) band. However, this scheme ignores the nonlinear spectral variation of broadband THz pulses, and its investigation of liquid water in a higher THz band (>1 THz) remains challenging until now. Here, we use <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -scan technology to directly measure the nonlinear absorption coefficient and nonlinear refractive index of liquid water excited at a higher THz range of 0.1–3 THz. Combined with THz time-domain spectroscopy technology, the spectral transmission characteristics caused by nonlinear effects in the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> -scan process are studied for the first time. The potential influence of the saturation absorption effect and self-phase modulation on the transmitted THz beam in liquid water are analyzed theoretically, and the origin of the nonlinear spectral distortion of the THz pulse is further revealed. This work offers a new perspective for observing the nonlinear transmission of THz pulses in liquid water and provides an experimental basis for more accurate analysis of the nonlinear characteristics of water-based THz devices in the future.

The topcoat thickness of thermal barrier coating (TBC) samples was measured using terahertz (THz) waves. The index of refraction of yttria stabilized zirconia (YSZ), which is the topcoat material, is necessary to obtain the topcoat thickness from time domain reflectometry. Time domain THz spectroscopy was applied to YSZ samples, and the index of refraction was measured to be 4.8 in the frequency region 0.1-1.2 THz. The topcoat thickness of 6 different TBC samples, which varied from 300 to 600 μm, was measured using THz waves. The results were in agreement with microscope observation results to within measurement error. In addition, the topcoat thickness profile of a turbine blade sample was measured with 2.4 μm resolution. The profile showed a standard deviation of 4 μm, which reflects the actual variation in the topcoat thickness. The results showed that THz waves are effective for high resolution measurement of the topcoat thickness.

Modulating terahertz (THz) waves actively and smartly through an external field is highly desired in the development of THz spectroscopic devices. Here, we demonstrate an active and smart electro-optic THz modulator based on a strongly correlated electron oxide vanadium dioxide (VO2). With milliampere current excitation on the VO2 thin film, the transmission, reflection, absorption, and phase of THz waves can be modulated efficiently. In particular, the antireflection condition can be actively achieved and the modulation depth reaches 99.9%, accompanied by a 180° phase switching. Repeated and current scanning experiments confirm the high stability and multibit modulation of this electro-optic modulation. Most strikingly, by utilizing a feedback loop of "THz-electro-THz" geometry, a smart electro-optic THz control is realized. For instance, the antireflection condition can be stabilized precisely no matter what the initial condition is and how the external environment changes. The proposed electro-optic THz modulation method, taking advantage of strongly correlated electron material, opens up avenues for the realization of THz smart devices.

The terahertz (THz) gap lying between the microwave and optical parts of the electromagnetic spectrum has attracted immense attention due to its applications between radiofrequency (RF)/microwave and photonic systems. A structure consisting of a graphene sheet sandwiched between two graphene disks is introduced herein to control the reflection, absorption, and transmission of THz waves. The proposed metamaterial structures are designed analytically using transmission line theory. Also, the dimensions of the structure and the electrical gating of the graphene are optimized utilizing a genetic algorithm. The structure is simulated using two different methods: (1) a circuit model based on transmission line theory and (2) commercial full-wave software based on the finite element method, which are verified by the agreement between their results. Finally, the proposed method is used to design a THz filter and THz wave absorber, which are in great demand for application in modulators, sensors, detectors, and imaging systems.

Linear optical absorption and terahertz (THz) sideband generation in quantum wells in the presence of a strong growth-direction oriented THz electric field is investigated. It is shown that the THz field can couple more than two levels simultaneously. The absorption spectra show a rich variety of behavior, including THz replicas of the 2 p exciton and THz sideband of the Is exciton. The THz electric field results in multiple optical absorption peaks due to resonant coupling between the valence subbands and produces splittings in the generated sidebands.