Low-cost calcium fluorometry for long-term nanoparticle studies in living cells

Calcium fluorometry is critical to determine cell homeostasis or to reveal communication patterns in neuronal networks. Recently, characterizing calcium signalling in neurons related to interactions with nanomaterials has become of interest due to its therapeutic potential. However, imaging of neuronal cell activity under stable physiological conditions can be either very expensive or limited in its long-term capability. Here, we present a low-cost, portable imaging system for long-term, fast-scale calcium fluorometry in neurons. Using the imaging system, we revealed temperature-dependent changes in long-term calcium signalling in kidney cells and primary cortical neurons. Furthermore, we introduce fast-scale monitoring of synchronous calcium activity in neuronal cultures in response to nanomaterials. Through graph network analysis, we found that calcium dynamics in neurons are temperature-dependent when exposed to chitosan-coated nanoparticles. These results give new insights into nanomaterial-interaction in living cultures and tissues based on calcium fluorometry and graph network analysis.

Development of rapid, sensitive and selective fluorimetric method for determination of 1-naphthalene acetic acid in cucumber by using magnetite-molecularly imprinted polymer

In this study, a novel method based on the determination of 1-naphthalene acetic acid with the usage of magnetite-molecularly imprinted polymer prior to fluorimetric detection has been developed. Magnetite-molecularly imprinted polymer has been used for the first time as selective adsorbent for the determination of 1-naphthalene acetic acid. The adsorption capacity of the synthesized polymer was found to be 2.18 ± 0.36 mg g^-1 (n = 3). Limit of detection (LOD) and limit of quantification (LOQ) of the method were found to be 0.75 and 2.50 μg L^-1, respectively. Linearity of the calibration graph for the proposed method was observed within the range of 20-700 μg L^-1. The proposed method seems to be rapid where the detection procedure for 1-naphthalene acetic acid can be completed within a total time of 1 h. The same imprinted polymer can be used for the determination of 1-naphthalene acetic acid with quantitative sorption and recovery values repeatedly for at least ten times. The effects of some potential organic interferences were investigated. Proposed method has been successfully applied to determine 1-naphthalene acetic acid in cucumber, where the recoveries of the spiked samples were found to be in the range of 93.7-104.5%. Characterization of the synthesized polymer was also evaluated. By combining the high capacity, cheapness, reusability and selectivity of the magnetic adsorbent with the dynamic calibration range, rapidity, simplicity, and sensitivity of fluorimetry, the proposed method seems to be an ideal method for the determination of trace levels of 1-naphthalene acetic acid.

Comparison of a Fluorimetric Method and a Competitive Protein Binding Assay Kit for the Determination of Plasma Hydroxycorticosteroids

A new competitive protein binding (C.P.B.) assay kit for the determination of plasma hydroxycorticosteroids which uses a gamma emitting isotope, selenium-75, to label the Cortisol was compared with a fluorimetric method in use in a routine laboratory. The mean plasma corticosteroid level in a group of 54 normal subjects was found to be lower with the C.P.B. kit than with the fluorimetric method. The correlation coefficient between the two methods in 131 specimens from healthy subjects and patients under investigation for pituitary or adrenocortical disorders was + 0.92. The precision of the two methods was similar.

A portable analyser for the measurement of ammonium in marine waters

A portable ammonium analyser was developed and used to measure in situ ammonium in the marine environment. The analyser incorporates an improved LED photodiode-based fluorescence detector (LPFD). This system is more sensitive and considerably smaller than previous systems and incorporates a pre-filtering subsystem enabling measurements in turbid, sediment-laden waters. Over the typical range for ammonium in marine waters (0–10 mM), the response is linear (r(2) = 0.9930) with a limit of detection (S/N ratio > 3) of 10 nM. The working range for marine waters is 0.05–10 mM. Repeatability is 0.3% (n =10) at an ammonium level of 2 mM. Results from automated operation in 15 min cycles over 16 days had good overall precision (RSD = 3%, n = 660). The system was field tested at three shallow South Florida sites. Diurnal cycles and possibly a tidal influence were expressed in the concentration variability observed.

Microfluorimeter with disposable polymer chip for detection of coeliac disease toxic gliadin

Coeliac disease is an inflammatory disease of the upper small intestine and results from gluten ingestion in genetically susceptible individuals, and is the only life-long nutrient-induced enteropathy. The only treatment is a strict gluten-free diet and the longer the individual fails to adhere to this diet, the greater the chance of developing malnutrition and other complications. The existence of reliable gluten free food is crucial to the well-being of the population. Here we report on a microfluorimeter device for the in situ detection of gliadin in foodstuffs, which could be used for a rapid control of raw materials in food processing, as well as for process control of gliadin contamination. The microfluorimeter is based on a reflector that is used inside a microfluidic chip, exploiting various strategically placed reflective or totally metallised mirrors for efficient collection of the fluorescent light emitted in a large solid angle. The chip is capable of executing five assays in parallel and has been demonstrated to possess detection sensitivity applicable to fluoroimmunoassays. Various immunoassay formats exploiting fluorescence detection, using enzyme/fluorophore labels were developed and compared in terms of sensitivity, ease of assay, assay time and compatibility with buffer used to extract gliadin from raw and cooked foodstuffs, with the best performance observed with an indirect competition assay using a fluorophore-labelled anti-mouse antibody. This assay was exploited within the microfluorimeter device, and a very low detection limit of 4.1 ng/mL was obtained. The system was observed to be highly reproducible, with an RSD of 5.9%, for a concentration of 50 ng/mL of gliadin applied to each of the five channels of the microfluorimeter. Biofunctionalised disposable strips incorporated into the microfluorimeter were subjected to accelerated Arrhenius thermal stability studies and it was demonstrated that strips pre-coated with gliadin could be stored for approximately 2 years at 4 degrees C, with no discernable loss in sensitivity or detectability of the assay. Finally, the microfluorimeter was applied to the analysis of commercial gluten-free food samples, and an excellent correlation with routine ELISA measurements was obtained. The developed microfluorimeter should find widespread application for on-site execution of fluoroimmunoassays.

A luminescence lifetime assisted ratiometric fluorimeter for biological applications

In general, the most difficult task in developing devices for fluorescence ratiometric sensing is the isolation of signals from overlapping emission wavelengths. Wavelength discrimination can be achieved by using monochromators or bandpass filters, which often lead to decreased signal intensities. The result is a device that is both complex and expensive. Here we present an alternative system--a low-cost standalone optical fluorimeter based on luminescence lifetime assisted ratiometric sensing (LARS). This paper describes the principle of this technique and the overall design of the sensor device. The most significant innovation of LARS is the ability to discriminate between two overlapping luminescence signals based on differences in their luminescence decay rates. Thus, minimal filtering is required and the two signals can be isolated despite significant overlap of luminescence spectra. The result is a device that is both simple and inexpensive. The electronic circuit employs the lock-in amplification technique for the signal processing and the system is controlled by an onboard microcontroller. In addition, the system is designed to communicate with external devices via Bluetooth.

A "Mix and Read" Assay for Insulin Using Fluorometric Microvolume Assay Technology

We describe a novel, "mix and read" immunoassay for insulin in biological samples using FMAT. Current commercial assays for insulin require multiple washing steps and can be expensive. The insulin assay described is a simple two-step, time-saving assay and amenable to robotics. The linear response for the fluorometric signal is comparable to that observed using classical ELISA and RIA. A series of mouse plasma samples were tested for insulin levels and yielded results comparable to that measured using a commercial ELISA for insulin.

Measurement of interferon-gamma by high-throughput fluorometric microvolume assay technology system

Interferon gamma (IFN-gamma) has various immunoregulatory effects and its measurement is widely used for monitoring immune response in many clinical trials for cancer vaccines. In this study, we developed a fluorescent-linked immunosorbent assay (FLISA) for the measurement of IFN-gamma. The FLISA can accurately measure IFN-gamma concentrations and the linear dynamic range of standard curve is 15.6-2000 pg/ml (2.1 log range). Because the FLISA needs only a small amount of antibodies and there is no washing process, it is able to reduce hands-on time and running costs compared with traditional enzyme-linked immunosorbent assay (ELISA). The FLISA can be readily performed in both 96- and 384-well plates, and up to 60 plates can be handled automatically by a robotic arm. Measurement of IFN-gamma by fluorometric microvolume assay technology (FMAT) may be a high-throughput screening method for a large number of samples.

Fluorescent staining of glycoproteins on polyvinylidene difluoride membrane with 8-aminonaphthalene-1,3,6-trisulfonate

Here, we describe a simple and sensitive method that allows fluorescent detection of glycoproteins on polyvinylidene difluoride (PVDF) membrane. We used periodic acid oxidation of carbohydrate chains of glycoproteins and fluorescent labeling with 8-aminonaphthalene-1,3,6-trisulfonate (AN-TS) by reductive amination. We developed an additional method to enhance the ability of PVDF to absorb glycoproteins by using non-glycoprotein lectin, such as wheat germ agglutinin (WGA), as a link between the PVDF membrane and glycoproteins, resulting in considerably increased detection sensitivity to glycoproteins.

Examination of four different instruments for measuring blood lactate concentration

Information on the performance of different instruments used to measure blood lactate concentration is incomplete. We therefore examined instruments from Yellow Springs Instruments (YSI 23L and YSI 1500) and three cheaper and simpler instruments: Dr. Lange's LP8+, Lactate Pro from Arkray in the KDK corporation and Accusport from Boehringer Mannheim. First, a number of blood samples were analysed by standard enzymatic photofluorometry (our reference method) and, in addition, by one or more of the instruments mentioned above. Second, measurements using two or more identical instruments were compared. Third, since Lactate Pro and Accusport are small (approximately 100 g, pocket-size), battery-driven, instruments that could be used for outdoor testing, the performance of these instruments was examined at simulated altitudes (O2 pressure of <10 kPa) and at temperatures below -20 degrees C, while screening the instruments as much as possible from the cold. Most of the different instruments showed systematically too high or too low values (10-25% deviation). The observed differences between instruments may affect the "blood lactate threshold" by 2-5%. We found different readings between "equal" YSI 1500 instruments, while we could see no difference when comparing the other instruments of the same type. Lactate Pro gave reliable results at both -21+/-1 degrees C and at simulated altitude. Accusport gave reliable results in the cold, but 1.85+/-0.08 mmol L(-1) (mean+/-SD) too high readings at the simulated altitude. Of the three simpler instruments examined, the Lactate Pro was at least as good as the YSI instruments and superior to the other two.

Flash fluorometer made from off-the-shelf photographic equipment to measure tissue levels of fluorescein

A device to measure fluorescein in tissue has been constructed from standard photographic equipment--an electronic strobe and a flashmeter both covered with interference filters. The instrument works well in the light and need not touch the area being measured, an advantage over existing fluorometers. The instrument has been used to measure the amount of dye in flaps in rats, pigs, and three humans. The results revealed that the amount of dye in a freshly made flap was rarely as much as in normal skin, and skin with less than 20 percent of the dye of control areas usually sloughed, although there were exceptions. In the future the instrument will be improved, and its readings will be compared to those obtained from radioactive microspheres, the present "gold standard" of techniques to measure vascularity. The instrument can be used to estimate the blood supply to any tissue and seems to be as reliable as the dermofluorometers already on the market.