An optical submicrometer calcium sensor with conductance sensing capability

A Wearable Electrochemical Platform for Noninvasive Simultaneous Monitoring of Ca(2+) and pH

Homeostasis of ionized calcium in biofluids is critical for human biological functions and organ systems. Measurement of ionized calcium for clinical applications is not easily accessible due to its strict procedures and dependence on pH. pH balance in body fluids greatly affects metabolic reactions and biological transport systems. Here, we demonstrate a wearable electrochemical device for continuous monitoring of ionized calcium and pH of body fluids using a disposable and flexible array of Ca(2+) and pH sensors that interfaces with a flexible printed circuit board. This platform enables real-time quantitative analysis of these sensing elements in body fluids such as sweat, urine, and tears. Accuracy of Ca(2+) concentration and pH measured by the wearable sensors is validated through inductively coupled plasma-mass spectrometry technique and a commercial pH meter, respectively. Our results show that the wearable sensors have high repeatability and selectivity to the target ions. Real-time on-body assessment of sweat is also performed, and our results indicate that calcium concentration increases with decreasing pH. This platform can be used in noninvasive continuous analysis of ionized calcium and pH in body fluids for disease diagnosis such as primary hyperparathyroidism and kidney stones.

Noninvasive monitoring of intracellular pH change induced by drug stimulation using silica nanoparticle sensors

We have synthesized and applied a nanoparticle-based pH sensor for noninvasive monitoring of intracellular pH changes induced by drug stimulation. The pH sensor is a two-fluorophore-doped nanoparticle sensor (2DFNS) that contains a pH-sensitive indicator (fluorescein isothiocyanate, FITC) and a reference dye (tris(2,2'-bipyridyl)dichlororuthenium(II) hexahydrate, RuBPY). The nanoparticles have an average diameter of 42 +/- 3 nm and can easily be taken up by cells for noninvasive intracellular pH measurement. The 2DFNS exhibited excellent pH sensitivity, reversibility, and a dynamic range of pH 4-7 for biological studies. We have used 2DFNS to monitor pH changes in living cells by drug stimulation. Both lysosomal pH changes in murine macrophages stimulated by chloroquine and intracellular acidification in apoptotic cancer cells were monitored in real time and with high pH sensitivity. Hela cells underwent intracellular acidification with a drop in pH from 7.2 to 6.5 after 8 h of treatment with 2 mumol/L dexamethasone, and this intracellular pH drop in the apoptotic cells was not influenced by the addition of zinc ions. The application of 2DFNS to intracellular pH measurements yields some important advantages: excellent pH sensitivity, little environmental effect on the pH dye, excellent quantification, high stability and excellent reversibility.

A Renewable Nanosensor Based on a Glass Nanopipette

A fluorescent nanosensor based on reporter dye molecules trapped in the tip of a nanopipette has been developed. This 100 nm sized nanosensor has been shown to be capable of measuring local pH and mapping sodium concentration with a temporal resolution of a few milliseconds.

Ion detection with photonic crystal microcavities

We have experimentally demonstrated a cation and anion sensor by using short linear photonic crystal microcavities with an embedded quantum dot active region. The photonic crystal microcavity covered with an ion-selective polymer forms a submicrometer optical detection system sensitive to small changes of perchlorate anion (ClO4(-)) and calcium cation (Ca2+) concentrations.

A single-channel method for evaluation of very magnitudes of Ca2+ ion fluxes through epsilon4/zeta1 N-methyl-D-aspartate receptor channels in bilayer lipid membranes

A single-channel method for evaluating agonist selectivity in terms of the very number of Ca2+ ions passed through the epsilon4/zeta1 N-methyl-D-aspartate (NMDA) receptor ion channel in bilayer lipid membranes (BLMs) is described. The number of Ca2+ passed through the single-channel was obtained from single-channel recordings in a medium where the primary permeant ion is Ca2+. The recombinant epsilon4/zeta1 NMDA channel was partially purified from Chinese hamster ovary cells expressing the channel and incorporated in BLMs formed by the tip-dip method. It was found that the epsilon4/zeta1 channel in BLMs is permeable to Ca2+ and Na+, but the number of Ca2+ passed through the channel is much fewer than that of Na+. The integrated Ca2+ currents induced by three typical agonists NMDA, L-glutamate and L-CCG-IV were obtained at concentration of 50 microM, where the integrated currents for all the agonists reached their saturated values. The integrated Ca2+ currents obtained are (3.1+/-0.21) x 10(-13) C/s for NMDA, (4.6+/-0.31) x 10(-13) C/s for L-glutamate and (5.7+/-0.25) x 10(-13) C/s for L-CCG-IV, respectively, suggesting that the three kinds of agonists have different efficacies to induce permeation of Ca2+. The range of the agonist selectivity thus obtained is much narrower than that of binding affinities for the NMDA receptors from rat brain. The present method is able to detect Ca2+ permeation with a detection limit of approximately 10(5) Ca2+ ions/s.

Synthesis and application of submicrometer fluorescence sensing particles for lysosomal pH measurements in murine macrophages

Phagocytosis of bioparticles such as bacteria and viruses by macrophages is a critical component of the immune response against infections. In this paper we describe the synthesis of submicrometer fluorescent particles with pH sensing capability. The particles are used to measure the pH and to monitor the effect of chloroquine, an antimalarial drug, on the pH in the lysosome, the cellular organelle involved in the phagocytosis process. The synthesis of the pH sensing particles is realized by the covalent attachment of amine reactive forms of Oregon Green (pH sensitive dye) and Texas Red (pH insensitive dye) to the surface of amino-modified submicrometer polystyrene particles. The particles are absorbed by J774 Murine Macrophages through phagocytosis and directed to lysosomes. Despite the high lysosomal levels of digestive enzymes and acidity, the absorbed particles remain stable for 12 h in the cells when they are stored in a PBS buffer solution at pH 7.4. The pH dynamic range of the sensing particles is between pH 4.5 and 7 with a sensitivity of 0.1 pH units. Exposure of the cells to chloroquine increases the lysosomal pH from 4.8 to 6.5. The effect is concentration-dependent.

Atomic force microscopy and other scanning probe microscopies

The highlight of the past year is the unfolding and refolding of the muscle protein titin in the atomic force microscope. A related highlight in the intersection between experiment and theory is a recent review of the effects of molecular forces on biochemical kinetics. Other advances in scanning probe microscopy include entropic brushes, molecular sandwiches and applications of atomic force microscopy to gene therapy.