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Taking advantage of the special Hg 2+ -promoted deprotection reaction of dithioacetals and the well-known coumarin chromophore, novel reactive fluorescent probes ( C3 and C4 ) towards mercury ions were designed and synthesized. Upon the addition of mercury ions, probe C3 displayed remarkable fluorescence quenching, which was beneficial to the production of a high signal output during sensing process. Differently, compound C4 displayed dramatic red-shift in both fluorescence (60 nm) and absorption (60 nm) spectra, with the detection limit of 90 nM. By virtue of this unique chemical reaction, compound C4 had selective response towards Hg 2+ over other metal ions and only the addition of Hg 2+ could lead to apparent emission and absorption spectra changes. Moreover, C4 was successfully applied to microscopic imaging for the detection of Hg 2+ in HeLa cells with ratiometric fluorescent methods. [ABSTRACT FROM AUTHOR]

pH-dependent protein adsorption on mesoporous silica nanoparticle (MSN) was examined as a unique means for pH monitoring. Assuming that the degree of protein adsorption determines the distance separating protein molecules, we examined the feasibility of nanoscale pH probes based on fluorescence resonance energy transfer (FRET) between two fluorescent proteins (mTurquoise2 and mNeonGreen, as donor and acceptor, respectively). Since protein adsorption on MSN is pH-sensitive, both fluorescent proteins were modified to make their isoelectric points (pIs) identical, thus achieving comparable adsorption between the proteins and enhancing FRET signals. The adsorption behaviors of such modified fluorescent proteins were examined along with ratiometric FRET signal generation. Results demonstrated that the pH probes could be manipulated to show feasible sensitivity and selectivity for pH changes in hosting solutions, with a good linearity observed in the pH range of 5.5-8.0. In a demonstration test, the pH probes were successfully applied to monitor progress of enzymatic reactions. Such an 'in situ-assembling' pH sensor demonstrates a promising strategy in developing nanoscale fluorescent protein probes. [ABSTRACT FROM AUTHOR]

This paper presents an ultra low-power and low-voltage pulse-width modulation based ratiometric capacitive sensor interface. The interface was designed and fabricated in a standard 90 nm CMOS 1P9M technology. The measurements show an effective resolution of 10 bits using 0.5 V of supply voltage. The active occupied area is only 0.0045 mm2 and the Figure of Merit (FOM), which takes into account the energy required per conversion bit, is 0.43 pJ/bit. Furthermore, the results show low sensitivity to PVT variations due to the proposed ratiometric architecture. In addition, the sensor interface was connected to a commercial pressure transducer and the measurements of the resulting complete pressure sensor show a FOM of 0.226 pJ/bit with an effective linear resolution of 7.64 bits. The results validate the use of the proposed interface as part of a pressure sensor, and its low-power and low-voltage characteristics make it suitable for wireless sensor networks and low power consumer electronics. [ABSTRACT FROM AUTHOR]

A universal pH indicator is used to fabricate a fiber optic ammonia sensor. The advantage of this pH indicator is that it exhibits sensitivity to ammonia over a broad wavelength range. This provides a differential response, with a valley around 500 nm and a peak around 650 nm, which allows us to perform ratiometric measurements. The ratiometric measurements provide not only an enhanced signal, but can also eliminate any external disturbance due to humidity or temperature fluctuations. In addition, the indicator is embedded in a hydrophobic and gas permeable polyurethane film named Tecoflex®. The film provides additional advantages to the sensor, such as operation in dry environments, efficient transport of the element to be measured to the sensitive area of the sensor, and prevent leakage or detachment of the indicator. The combination of the universal pH indicator and Tecoflex® film provides a reliable and robust fiber optic ammonia sensor. [ABSTRACT FROM AUTHOR]

Highlights: [•] Triple-labeled polyelectrolyte microcapsule pH sensors were fabricated. [•] The capsules can be used for ratiometric pH sensing with a wide dynamic pH measurement range. [•] The capsules can report the local pH environment when ingested by cells. [•] The capsules are finally accumulated in acidic environments in cells. [Copyright &y& Elsevier]