Terahertz spectra of proteinuria and non-proteinuria.

In clinical practice, proteinuria detection is of great significance in the diagnosis of kidney diseases. Dipstick analysis is used in most outpatient settings to semi-quantitatively measure the urine protein concentration. However, this method has limitations for protein detection, and alkaline urine or hematuria will cause false positive results. Recently, terahertz time-domain spectroscopy (THz-TDS) with strong hydrogen bonding sensitivity has been proven to be able to distinguish different types of biological solutions, which means that protein molecules in urine may have different THz spectral characteristics. In this study, we performed a preliminary clinical study investigating the terahertz spectra of 20 fresh urine samples (non-proteinuria and proteinuria). The results showed that the concentration of urine protein was positively correlated with the absorption of THz spectra at 0.5-1.2 THz. At 1.0 THz, the pH values (6, 7, 8, and 9) had no significant effect on the THz absorption spectra of urine proteins. The terahertz absorption of proteins with a high molecular weight (albumin) was greater than that of proteins with a low molecular weight (ß2-microglobulin) at the same concentration. Overall, THz-TDS spectroscopy for the qualitative detection of proteinuria is not affected by pH and has the potential to discriminate between albumin and ß2-microglobulin in urine.

Terahertz spectroscopic monitoring and analysis of citrus leaf water status under low temperature stress.

Low temperature stress, in the form of chilling and freezing, is one of the major environmental factors impacting on citrus yield, which changes plant's water state and results in the crops' sub-health or injury. The innovative terahertz (THz) spectroscopy and imaging based sensing technology has been shown to be a suitable tool for plant leaf water status determination, due to THz radiation's innate sensitivity to hydrogen bond vibration in aqueous solutions, which is usually related to plant phenotype change. We demonstrate experimentally that the THz absorption coefficient of leaf could be used for distinguishing plant's physiological stress status, exhibiting clear decreasing or increasing trend under chilling or freezing stress respectively. The underlying rationale might be that membrane damage shows a diverse pattern, changing the intra- or extra-cellular liquid environments, likely being linked to the various THz spectral characteristics. There were different adaptations in leaf morphology, leading to different leaf density, which in turn affects the water volume fraction. Moreover, different patterns of the dynamic equilibrium state of free water and bound water under chilling and freezing treatment were revealed by THz spectroscopy. Here, THz spectroscopic monitoring has shown unique potential for judging citrus's low temperature stress state through bio-water detection and discrimination.

Single cell imaging with near-field terahertz scanning microscopy.

OBJECTIVES: Terahertz (THz)-based imaging techniques hold great potential for biological and biomedical applications, which nevertheless are hampered by the low spatial resolution of conventional THz imaging systems. In this work, we report a high-performance photoconductive antenna microprobe-based near-field THz time-domain spectroscopy scanning microscope. MATERIALS AND METHODS: A single watermelon pulp cell was prepared on a clean quartz slide and covered by a thin polyethylene film. The high performance near-field THz microscope was developed based on a coherent THz time-domain spectroscopy system coupled with a photoconductive antenna microprobe. The sample was imaged in transmission mode. RESULTS: We demonstrate the direct imaging of the morphology of single watermelon pulp cells in the natural dehydration process with our near-field THz microscope. CONCLUSIONS: Given the label-free and non-destructive nature of THz detection techniques, our near-field microscopy-based single-cell imaging approach sheds new light on studying biological samples with THz.

Terahertz spectral imaging based quantitative determination of spatial distribution of plant leaf constituents.

BACKGROUND: Plant leaves have heterogeneous structures composed of spatially variable distribution of liquid, solid, and gaseous matter. Such contents and distribution characteristics correlate with the leaf vigor and phylogenic traits. Recently, terahertz (THz) techniques have been proved to access leaf water content and spatial heterogeneity distribution information, but the solid matter content and gas network information were usually ignored, even though they also affect the THz dielectric function of the leaf. RESULTS: A particle swarm optimization algorithm is employed for a one-off quantitative assay of spatial variability distribution of the leaf compositions from THz data, based on an extended Landau-Lifshitz-Looyenga model, and experimentally verified using Bougainvillea spectabilis leaves. A good agreement is demonstrated for water and solid matter contents between the THz-based method and the gravimetric analysis. In particular, the THz-based method shows good sensitivity to fine-grained differences of leaf growth and development stages. Furthermore, such subtle features as damages and wounds in leaf could be discovered through THz detection and comparison regarding spatial heterogeneity of component contents. CONCLUSIONS: This THz imaging method provides quantitative assay of the leaf constituent contents with the spatial distribution feature, which has the potential for applications in crop disease diagnosis and farmland cultivation management.

Label-free protein detection using terahertz time-domain spectroscopy.

Protein analysis is the foundation to understanding the mechanisms of complex biological processes. As one of the most widely used techniques to determine protein species and contents, protein dot blot aids biology research but needs corresponding antibodies for marking. A label-free detection method based on terahertz time-domain spectroscopy (THz-TDS) is proposed and demonstrated to improve this traditional technology. A membrane loaded with protein samples is directly scanned using a transmission THz-TDS system for spectral imaging. Different kinds of proteins can be distinguished by the refractive index extracted from the THz transmission spectrum. The intensity or shade imaged with the THz transmission spectrum can help detect the protein quantitatively. The feasibility of this new protein assay is demonstrated by the results of systematic testing with actual samples prepared with the dot-blot protocol.