Dual fluorescent hollow silica nanofibers for in situ pH monitoring using an optical fiber

This study reports a sensitive and robust pH sensor based on dual fluorescent doped hollow silica nanofibers (hSNFs) for in situ and real-time pH monitoring. Fluorescein isothiocyanate (FITC) and tris(2,2'-bipyridyl)dichlororuthenium(ii) hexahydrate (Ru(BPY)3) were chosen as a pH sensitive dye and reference dye, respectively. hSNFs were synthesized using a two-step method in a reverse micelle system and were shown to have an average length of 6.20 μm and average diameter of 410 nm. The peak intensity ratio of FITC/Ru(BPY)3 was used to calibrate to solution pH changes. An optical-fiber-based fluorescence detection system was developed that enabled feasible and highly efficient near-field fluorescence detection. The developed system enables fully automated fluorescence detection, where components including the light source, detector, and data acquisition unit are all controlled by a computer. The results show that the developed pH sensor works in a linear range of pH 4.0-9.0 with a fast response time of less than 10 s and minimal sample volume of 50 μL, and can be stored under dark conditions for one month without failure. In addition, the as-prepared hSNF-based pH sensors also have excellent long-term durability. Experimental results from ratiometric sensing confirm the high feasibility, accuracy, stability and simplicity of the dual fluorescent hSNF sensors for the detection of pH in real samples.

Exploring Idiopathic Pulmonary Fibrosis Biomarker by Simultaneous Two-Photon Fluorescence Imaging of Cysteine and Peroxynitrite

Idiopathic pulmonary fibrosis (IPF) has been characterized as a chronic inflammatory disease that leads to irreversible damage to pulmonary function. However, there is no specific IPF biomarker that can be used to distinguish IPF and not pneumonia. Endoplasmic reticulum (ER) stress is prominent in IPF. To search for a specific biomarker of IPF, we developed two ER-targeting two-photon (TP) fluorescent probes, TP^ER-ONOO and TP^ER-Cys, for peroxynitrite (ONOO^-) and cysteine (Cys) imaging, respectively. A significant increase in Cys levels in the lungs was discovered only in mice with IPF, which implied that Cys might be an IPF biomarker candidate. Furthermore, we uncovered the mechanism of glutathione (GSH) deficiency in IPF, which was not due to Cys shortage but instead was attributable to impaired glutamate cysteine ligase and glutathione synthetase activities via ONOO^--induced post-transcriptional modification. This work has potential to provide a new method for IPF early diagnosis and drug efficacy evaluation.

Review: Nanomaterials for Reactive Oxygen Species Detection and Monitoring in Biological Environments

Reactive oxygen species (ROS) and dissolved oxygen play key roles across many biological processes, and fluorescent stains and dyes are the primary tools used to quantify these species in vitro. However, spatio-temporal monitoring of ROS and dissolved oxygen in biological systems are challenging due to issues including poor photostability, lack of reversibility, and rapid off-site diffusion. In particular, ROS monitoring is hindered by the short lifetime of ROS molecules and their low abundance. The combination of nanomaterials and fluorescent detection has led to new opportunities for development of imaging probes, sensors, and theranostic products, because the scaffolds lead to improved optical properties, tuneable interactions with cells and media, and ratiometric sensing robust to environmental drift. In this review, we aim to critically assess and highlight recent development in nanosensors and nanomaterials used for the detection of oxygen and ROS in biological systems, and their future potential use as diagnosis tools.

Stability and Performance Study of Fluorescent Organosilica pH Nanosensors

Long-term stability and function are key challenges for optical nanosensors operating in complex biological environments. While much focus is rightly placed on issues related to specificity, sensitivity, reversibility, and response time, many nanosensors are not capable of transducing accurate results over prolonged time periods. Sensors could fail over time due to the degradation of scaffold material, degradation of signaling dyes and components, or a combination of both. It is critical to investigate how such degradative processes affect sensor output, as the consequences could be severe. Herein, we used fluorescent core-shell organosilica pH nanosensors as a model system, incubating them in a range of common aqueous solutions over time at different temperatures, and then searched for changes in fluorescence signal, particle size, and evidence of silica degradation. We found that these ratiometric nanosensors produced stable optical signals after aging for 30 days at 37 °C in standard saline buffers with and without 10% fetal bovine serum, and without any evidence of material degradation. Next, we evaluated their performance as real-time pH nanosensors in bacterial suspension cultures, observing a close agreement with a pH electrode for control nanosensors, yet observing obvious deviations in signal based on the aging conditions. The results show that while the organosilica scaffold does not degrade appreciably over time, careful selection of dyes and further systematic investigations into the effects of salt and protein levels are required to realize long-term stable nanosensors.

Meso-Substituent-Directed Aggregation Behavior and Water Solubility: Direct Functionalization of Methine Chain in Thiazole Orange and Biological Applications in Aqueous Buffer

A new strategy is presented to preclude aggregation and enhance water solubility of cyanine dyes. Namely, a heteroatom-containing substituent, for distorting molecular plane and increasing interaction with water molecules, is introduced to the methine chain of 2-thiazole orange (1, a monocyanine) via one-step, and 2-thiazole orange derivatives 2a-g are prepared accordingly. The X-ray crystal structures show that the molecular plane of 2a-g is drastically twisted, which reduces intermolecular π-π stacking. The derivatives 2a-g exhibit good to excellent water solubility and can be dissolved in aqueous phosphate-buffered saline (PBS) at concentrations suitable for biomedical applications. No aggregation in aqueous PBS, relatively high molar extinction coefficients, and low solvatochromism of 2a-g are reflected by the UV-vis spectra. Compound 2b shows fast response and high selectivity for biothiols (Cys, Hcy, and GSH) in aqueous PBS and is further employed to detect endogenous biothiols with decent biocompatibility as demonstrated by live cell fluorescence imaging.