Here, a novel sensor NS for NH 4 + was designed based on the concept of dynamic equilibrium between NH 4 + and NH 3 .

There is an increasing demand for sensitive, selective, and convenient detection tools for disease-related biomarker, potassium ion (K+). Electrospinning nanofibrous film as a novel sensing platform exhibits unique advantages due to high surface area ratio and network structure. In this study, electrospinning technique was employed to construct poly(vinyl alcohol) (PVA) nanofibrous film to assist K+ sensing. To find the best recipe, these factors including probe concentration, solvent composition, spinning time and cross-linking time were explored, and 8 groups of sensing films (F0-F7) were obtained in which F2 was considered the best and used for subsequent tests. Under optimized conditions, the sensing platform F2 was constructed by relatively continuous, uniform fibers with diameters in the range of 150???250 nm, and showed excellent selectivity, reusability, considerable response speed, and high sensitivity in which the fluorescence enhanced factor was as high as 8.9 with 10 mM K+. Moreover, F2 showed high accuracy in real samples detection, and it was used as a real-time K+ sensing platform. The excellent performance of F2 not only proved the reasonable design principle using PVA fibers for K+ sensing, but also could be extended to other probes and lead to different selectivity which was significant for biological diagnosis.

The concentration of potassium ion is an important indicator for human health, and its abnormality is often accompanied by various diseases. However, most tools currently used to study potassium ion transport are low throughput. Herein, we reported a new K+ fluorescent nanoprobe CP1-KS with high selectivity and sensitivity to K+ (fluorescence enhanced factor was up to 9.91 at 20 mM K+). The polymeric fluorescent probe CP1-KS was composed of the small-molecular K+ indicator KS and amphiphilic copolymer CP1. This sensor can be easily and uniformly dispersed in cell culture medium and is suitable for high throughput analysis. To assess the utility of the probe CP1-KS in biological field, this probe was employed as an extracellular fluorescent probe to monitor the efflux of K+ from cells (E coli, B. Subtilis 168, Hela and MCF-7 cells) under various stimulation including lysozyme, nigericin, digitonin, and ATP. Results demonstrated that CP1-KS is an effective analysis tool for extracellular K+ concentration. We believe that the nanoprobe has great potential in antibacterial drug screening, K+ ionophore function, K+ channel activity, cell membrane permeability analysis or other K+ related field in the future.

Dysfunction of potassium ion (K+) channels are closely related to various diseases, while the current tools for studying K+ channels are indirect methods that cannot measure the flux of K+ in live cells. Herein, we prepared K+ fluorescent nanoprobes (KFK-Cat NPs) with appropriate dissociation constant (K-d) value (127 mM K+) and excellent stability, especially photostability, for intracellular K+ sensing and imaging. An easy-operating and biocompatible method for functional measurement of human ether-a-go-go-related gene (hERG) channel activity was constructed via directly monitoring the fluctuation of K+ in KFK-Cat NPs stained hERG-HEK293 cells. Further, this method was efficient for screening of hERG channel inhibitors, the results were in accordance with the traditional patch-clamp technique and the commercially available thallium ion (Tl+) fluorescent probes assay kits. The KFK-Cat NPs were also capable of K+ imaging after endocytosed by hERG-overexpressing colon cancer cells. This work, for the first time, broadens the application of K+ fluorescent probes for functional analysis of K+ channels activity under the help of confocal laser scanning microscope (CLSM). This method shows significant potentials for drug screening and provides efficient tool for deep investigation of K+ channel-related diseases, including tumor.

Two new block copolymers (P1 and P2) containing platinum porphyrin-based phosphorescent probes with different molar ratios of polydimethylsiloxane (PDMS) and isobutyl methacrylate (IBM) were successfully synthesized via atom transfer radical polymerization (ATRP) with narrow polydispersity smaller than 1.21. For comparison, P3 without the PDMS block was also prepared. Results of 1H NMR and GPC demonstrated their successful preparation. Oxygen sensing performance and pressure sensitivity of these polymers were investigated. Results showed that the polymer with more PDMS contents exhibited higher oxygen sensitivity, better pressure sensitivity, and faster response time. The pressure sensitivity of polymer with more PDMS contents was affected more significantly by temperature. The polymer P1 with a fraction of PDMS of 50 wt% reported herein showed a high pressure sensitivity of 0.82%/kPa, which is among the highest ones of the reported polymers. These results may provide helpful information for broadening the development of oxygen sensors and pressure sensitive paints.

We report on the fabrication of K+ fluorescent sensor P2 based on thermoresponsive poly(N-isopropylacrylamide) and small molecule K+ fluorescent sensor KS. P2 changed its size with a range from 35 degrees C to 42 degrees C and exhibited lower critical solution temperature (LCST) at 38 degrees C. The LCST affected the polymer's nanostructures and microenvironment of KS, which in turn affected P2's fluorescence intensities and responses to K+. Furthermore, P2 exhibited high selectivity and sensitivity to K+ with a dynamic response range from 1 to 20 mM, enabling its suitableness for extracellular K+ analysis. The sensor was further used to in situ monitor the K+ fluctuation of Escherichia coli and B. Subtilis 168 bacteria under lysozyme stimulation in 96 well plate by a high throughput analysis approach, and cell species dependent K+ release was observed. The PNIPAM-based K+ sensor P2 shows potential application in antimicrobial drugs/peptides screening.

Highly selective fluorescent K+ sensors are of great importance for monitoring K+ fluctuations in various biological processes. In particular, highly efficient ratiometric K+ sensors that can emit in dual wavelengths and facilitate the quantitative determination of K+ are highly anticipated. Herein, we present the first polymer-based ratiometric fluorescent K+ indicator (PK1) for quantitatively detecting K+ in aqueous solutions and high-throughput monitoring K+ fluctuations in living cells. PK1 was synthesized by conjugating a small molecular K+ probe and a red emission reference dye to a hydrophilic polymer skeleton. The newly synthesized PK1 can form highly stable nanoparticles in aqueous solutions and work in 100% water without the aid of any organic solvents or surfactants. PK1 is sensitive to K+ with a fluorescence enhancement of sevenfold after interactions with K+ at 1000 mM and inert to other metal ions, physiological pH, or dye concentration vibrations. More importantly, the fluorescence intensity ratio at 572 and 638 nm is linearly correlated with log [K+] in the range of 2-500 mM (R2 = 0.998), which will facilitate the quantitative detection of K+. Practical application of PK1 in detecting different K+-rich samples demonstrates its great potential in quantitative detection of K+. PK1 can be quickly internalized by live cells and shows no obvious cytotoxicity. We also demonstrate that PK1 could be used for monitoring K+ fluctuations under different stimulations by using a confocal microscope and especially a microplate reader, which is high throughput and time saving. The rational design of PK1 will broaden the design concept of ratiometric fluorescent K+ sensors and facilitate the quantitative detection of K+.