Метод импедансной спектроскопии для тестирования увлажненных зерен пшеницы

The authors presented the results of a study of the electrical and dielectric characteristics of wetted wheat grains by measuring their complex electrical resistance (impedance Z) in a wide frequency range (from 1 Hz to 100 MHz). The results of electrical impedance measurements of grains with surface or volumetric moisture content under different experimental conditions can provide useful information on the properties of the biological tissues of grain crops. These results can also be used to develop a new type of impedance sensor for testing grain quality and moisture content. The authors used well-dried wheat grains and grains saturated with moisture and saline as objects of research. A major problem in grain impedance measurements is the selection of a suitable electrode material to be placed on the end surfaces of the samples. The electrodes must ensure reliable contact with the grain and have a minimum transient resistance. The end surfaces of the pressed samples were reinforced with a protective dielectric ring to prevent transverse deformation. These contacts provided a transition resistance between 1-2 ohms. The authors have identified processes of accumulation of electric charges near the surface of metal electrodes at low frequencies and on internal grain structures, leading to an increase in the dielectric permittivity and dissipation factor. The behavior of the active and reactive components of the impedance at higher frequencies is determined by dielectric relaxation processes. The obtained impedance spectra were compared with the spectra of the most suitable equivalent electrical circuits. The radio components of the circuits provide information about the basic mechanisms of alternating electric current flow through the complex inhomogeneous structure of the grain. The authors found that moistening the grain with saline water enhances the process of accumulation of electric charges and affects the dispersion of the real and imaginary components of the impedance.Представлены результаты исследования электрических и диэлектрических характеристик увлажнённых зёрен пшеницы методом измерений их комплексного электрического сопротивления (импеданса Z) в широком диапазоне частот (от 1 Гц до 100 МГц). Результаты измерений электрического импеданса зерна с поверхностным или объёмным содержанием влаги в разных условиях эксперимента могут дать полезную информацию о свойствах биологических тканей зерновых культур и использоваться для разработки нового типа импедансных датчиков для тестирования качества зерна и его влажности. В качестве объекта исследований использовались хорошо высушенные зёрна пшеницы и зёрна, насыщенные влагой и солевым раствором. Серьёзной проблемой при измерениях импеданса зёрен является выбор подходящего материала электродов, накладываемых на торцевые поверхности образцов. Электроды должны обеспечивать надёжный контакт с зерном и обладать минимальным переходным сопротивлением. Для исключения поперечной деформации торцевые поверхности прессованных образцов укрепляли защитным диэлектрическим кольцом. Такие контакты обеспечивали переходное сопротивление в пределах 1–2 Ом. В области низких частот выявлены процессы накопления электрических зарядов вблизи поверхности металлических электродов и на внутренних структурах зерна, приводящие к увеличению диэлектрической проницаемости и тангенса угла потерь. В области более высоких частот поведение активной и реактивной компонент импеданса определяется процессами диэлектрической релаксации. Полученные спектры импеданса сопоставлялись со спектрами наиболее подходящих эквивалентных электрических схем, радиотехнические компоненты которых позволяют понять основные механизмы прохождения переменного электрического тока через сложную неоднородную структуру зерна. Установлено, что увлажнение зерна подсоленной водой усиливает процесс накопления электрических зарядов и влияет на дисперсию действительной и мнимой компонент импеданса

Facile Synthesis of Amine-Functionalized Eu3+-Doped La(OH)3 Nanophosphors for Bioimaging

Here, we report a straightforward synthesis process to produce colloidal Eu3+-activated nanophosphors (NPs) for use as bioimaging probes. In this procedure, poly(ethylene glycol) serves as a high-boiling point solvent allowing for nanoscale particle formation as well as a convenient medium for solvent exchange and subsequent surface modification. The La(OH)3:Eu3+ NPs produced by this process were ~3.5 nm in diameter as determined by transmission electron microscopy. The NP surface was coated with aminopropyltriethoxysilane to provide chemical functionality for attachment of biological ligands, improve chemical stability and prevent surface quenching of luminescent centers. Photoluminescence spectroscopy of the NPs displayed emission peaks at 597 and 615 nm (λex = 280 nm). The red emission, due to 5D0 → 7F1 and 5D0 → 7F2 transitions, was linear with concentration as observed by imaging with a conventional bioimaging system. To demonstrate the feasibility of these NPs to serve as optical probes in biological applications, an in vitro experiment was performed with HeLa cells. NP emission was observed in the cells by fluorescence microscopy. In addition, the NPs displayed no cytotoxicity over the course of a 48-h MTT cell viability assay. These results suggest that La(OH)3:Eu3+ NPs possess the potential to serve as a luminescent bioimaging probe

Competitive quenching fluorescence immunoassay for chlorophenols based on laser-induced fluorescence detection in microdroplets

8 pages, 7 figures, 1 table.-- PMID: 12530822 [PubMed].-- Available online Nov 2, 2002.An improved biomonitoring system for the analysis of 2,4,6-trichlorophenol (TCP) in urine samples has been developed. The principle of the biosensor device is the detection of laser-induced fluorescence (LIF) in single microdroplets by a homogeneous quenching fluorescence immunoassay (QFIA). The competitive immunoassay occurs in microdroplets (d = 58,4 μm) produced by a piezoelectric generator system with 10-μm-diameter orifice. A continuous Ar ion laser (488 nm) excites the fluorescent tracer; its fluorescence is detected by a spectrometer attached to a 512 × 512 cooled, charge-coupled device camera. Fluorescence is quenched by specific binding of TCP polyclonal antibodies to the fluorescent tracer (hapten A−fluorescein); the quenching effect is diminished by the presence of the analyte. Thus, an increase in the signal is produced in a positive dose-dependent manner when TCP is present in the sample. In 10 mM PBS buffer, the IC50 of the LIF-microdroplet QFIA is 0.45 μg L-1 reaching a LOD of 0.04 μg L-1. The QFIA with the same reagents performed in microtiter plate format achieved a LOD of 0.36 μg L-1 in buffer solution. Performance in human urine was similar to that observed in the buffer. A LOD of 1.6 μg L-1, with a dynamic range between 4 and 149.5 μg L-1 in urine, was obtained without any sample treatment other than dilution with the assay buffer. The detectability achieved is sufficient for occupational exposure risk assessment.This research was supported by the Superfund Basic Research Program from the National Institute of Environmental Health Sciences (Grant 5P42ES04699, NIH with funding provided by EPA), by the EC Program (Contract QLRT-2000-01670), and by the Spanish Government through CICYT (BIO2000-0351-P4-05). UCD is a NIEHS Environmental Health Center P30 ESO5707.Peer reviewe