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.

Real-time monitoring of dissolved oxygen (DO) and pH is of great significance for understanding cellular metabolism. Herein, a dual optical pH/O2 sensing membrane was prepared by the electrospinning method. Cellulose acetate (CA) and poly(ε-caprolactone) (PCL) nanofiber membrane blended with platinum (II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorophenyl)-porphyrin (PtTFPP) was used as the DO sensing matrix, upon which electrospun nanofiber membrane of chitosan (CS) coupled with fluorescein 5-isothiocyanate (FITC) was used as the pH sensing matrix. The electrospun sensing film prepared from biocompatible biomaterials presented good response to a wide range of DO concentrations and physiological pH. We used it to monitor the exracellular acidification and oxygen consumption levels of cells and bacteria. This sensing film can provide a luminescence signal change as the DO and pH change in the growth microenvironment. Due to its advantages of good biocompatibility and high stability, we believe that the dual functional film has a high value in the field of biotechnology research.

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.

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+.

A new simple mitochondria-targeted fluorescent potassium ion (K+) sensor (NK1) was synthesized and investigated. The synthetic route of this sensor was much more concise than the previously reported mitochondrial-targeting KS6, enabling the potential broad applications of this sensor NK1. NK1 displays good responses to K+ with broad detection range from 10 to 500 mM, short response time (0.2 s), high sensitivity with 160 folds' fluorescence enhancement at 1000 mM K+, a large dissociation constant (K-d about 200 mM), and minimum responses to physiological pH (5.0-9.0) as well as other biologically relevant metal ions. K+ fluxes (efflux and influx) in the mitochondria of living cells were observed upon manipulation with ionophores (nigericin or ionomycin) and various concentrations of KCl both under confocal microscope and especially microplate reader for first time high-throughput in-situ monitoring of mitochondrial K+ fluxes. The development of easily synthesized NK1 with excellent performance will be greatly beneficial for ion channel relative drug screening and the investigation of mitochondrial potassium channels as well as mitochondrial metabolism.

The first NIR fluorescent mitochondria-targeting K+ sensor, denoted as TAC-Rh, was developed. The produced sensor consists of a rhodamine analog as the fluorophore and triazacryptand (TAC) as the K+ recognition unit. Compared to the K+ sensors reported previously, TAC-Rh exhibits two unique optical properties: the largest Stokes shifts (120 nm) and the longest emission peak wavelength (720 nm). With the assistance of this novel sensor, real-time changes of K+ concentrations in mitochondria during apoptosis were monitored for the first time. Moreover, it was also the first time that the relationship between mitochondrial K+ flux and apoptosis was investigated in real time using fluorescence imaging.

The potassium ion (K+) plays significant roles in many biological processes. To date, great efforts have been devoted to the development of K+ sensors for colorimetric, fluorescent, and photoacoustic detection of K+ separately. However, the development of molecular K+ probes for colorimetric detection of urinary K+, monitoring K+ fluxes in living cells by fluorescence imaging, and photoacoustic imaging of K+ dynamics in deep tissues still remains an open challenge. Herein, we report the first molecular K+ probe (NK2) for colorimetric, fluorescent, and photoacoustic detection of K+. NK2 is composed of 2-dicyanomethylene-3-cyano-4,5,5-trimethyl-2,5-dihydrofuran (TCF) as the chromophore and phenylazacrown-6-lariat ether (ACLE) as the K+ recognition unit. Predominate features of NK2 include a short synthetic procedure, high K+ selectivity, large detection range (5–200 mM), and triple-channel detection manner. NK2 shows good response to K+ with obvious color changes, fluorescence enhancements (about threefold), and photoacoustic intensity changes. The existence of other metal ions (including Na+, Mg2+, Ca2+, Fe2+) and pH changes (6.5–9.0) have no obvious influence on K+ sensing of NK2. Portable test strips stained by NK2 can be used to qualitatively detect urinary K+ by color changes for self-diagnosis of diseases induced by high levels of K+. NK2 can be utilized to monitor K+ fluxes in living cells by fluorescent imaging. We also find its excellent performance in photoacoustic imaging of different K+ concentrations in the mouse ear. NK2 is the first molecular K+ probe for colorimetric, fluorescent, and photoacoustic detection of K+ in urine, in living cells, and in the mouse ear. The development of NK2 will broaden K+ probes’ design and extend their applications to different fields.

Root hair elongation relies on polarized cell expansion at the growing tip. As a major osmotically active ion, potassium is expected to be continuously assimilated to maintain cell turgor during hair tip growth. However, due to the lack of practicable detection methods, the dynamics and physiological role of K+ in hair growth are still unclear. In this report, we apply the small-molecule fluorescent K+ sensor NK3 in Arabidopsis root hairs for the first time. By employing NK3, oscillating cytoplasmic K+ dynamics can be resolved at the tip of growing root hairs, similar to the growth oscillation pattern. Cross-correlation analysis indicates that K+ oscillation leads the growth oscillations by approximately 1.5 s. Artificially increasing cytoplasmic K+ level showed no significant influence on hair growth rate, but led to the formation of swelling structures at the tip, an increase of cytosolic Ca2+ level and microfilament depolymerization, implying the involvement of antagonistic regulatory factors (e.g., Ca2+ signaling) in the causality between cytoplasmic K+ and hair growth. These results suggest that, in each round of oscillating root hair elongation, the oscillatory cell expansion accelerates on the heels of cytosolic K+ increment, and decelerates with the activation of antagonistic regulators, thus forming a negative feedback loop which ensures the normal growth of root hairs.

A potassium ion‑oxygen (K+–O2) dual fluorescent sensing film was developed. The film contains three probes, which are K+ probe (KS), O2 probe (OS), and reference probe (RP) in a polymer film composed of poly(ethylene glycol) methyl ether methacrylate (PEGMA), poly(ethylene glycol) dimethacrylate (PEGDMA) and methacrylic acid (MAA). The RP showed blue emission, the KS exhibited green emission, and the OS showed red emission. The emission peaks of three probes do not interfere with each other, which enable the sensing film to be used for ratiometrically and quantitatively detecting the concentrations of K+ and dissolved oxygen (DO). The sensing films showed high sensitivity and selectivity to potassium ions over other metal ions and also good sensitivity for DO from deoxygenated to oxygenated conditions. The sensing film was demonstrated to be capable of analyzing K+ and DO concentrations with experimental errors smaller than ±8.5% in aqueous solutions, showing the potential applications of the sensing films.

The future of personalized cancer treatments relies on the development of functional agents that have tumor-targeted anticancer activities and can be detected in tumors using imaging. However, application of these functional agents in the clinic has been limited due to inefficient drug delivery, low specificity for tumor imaging, development of drug resistance, low signal-to-noise ratio and safety concerns regarding potential toxicity. Currently, the most common strategy to develop these functional agents is to conjugate therapeutic agents with the appropriate fluorescent probe. The present study synthesized a novel mitochondria-targeted heptamethine cyanine (Cy) derivative Cy‑triphenylphosphonium. The newly developed compound exhibited stronger near infrared (NIR) fluorescence and reacted with bovine serum albumin. In addition, it preferentially accumulated in the mitochondria of cancer cells, as observed using confocal microscopy, and efficiently reduced cancer cell viability (IC50=3.04 µM). This novel multifunctional heptamethine Cy derivative, with cancer mitochondria targeting and NIR fluorescence imaging, may be promising as an alternative anticancer agent.

To improve the effect of thrombosis therapy, an amphiphilic supramolecular prodrug consisting of diosgenin derivative (theophylline–diosgenin) and uracil-terminated poly(ethylene glycol) (PEG-U) was designed and synthesized successfully.