A series of simple curcumin-derived colorimetric and fluorescent probes for ratiometric-pH sensing and cell imaging

pH-Responsive Fluorescent Switches through Intramolecular Conjugate Addition Reactions and Application in Fluorogenic Bioimaging

We report new photoluminescent switching systems achieved through pH-induced intramolecular oxa-Michael conjugate addition reactions. Ratiometric absorbance and fluorescence emission were observed across conjugate acceptors triggered by pH, resulting in specific pseudo pKa values. The effect of substituents on the pseudo pKa's was investigated, showing increased values from electron-withdrawing to electron-donating groups. Inspired by the physiologically related pKa, a fluorescent probe was designed, successfully distinguishing cancer cells from normal cells through live cellular imaging.

Organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH for biosensing, bioimaging and biotherapeutics applications

In recent years, organic fluorophores-based molecular probes with dual-fluorescence ratiometric responses to in-vitro/in-vivo pH (DFR-MPs-pH) have been attracting much interest in fundamental application research fields. More and more scientific publications have reported the exploration of various DFR-MPs-pH systems that have unique dual-fluorescence ratiometry as the signal output, in-built and signal self-calibration functions to improve precise detection of targets. DFR-MPs-pH systems possess high-performance applications in biosensing, bioimaging and biomedicine fields. This review has comprehensively summarized recent advances of DFR-MPs-pH for the first time. First of all, the compositions and types of DFR-MPs-pH are introduced by summarizing different organic fluorophores-based molecule systems. Then, construction strategies are analyzed based on specific components, structures, properties and functions of DFR-MPs-pH. Afterward, biosensing and bioimaging applications are discussed in detail, primarily referring to pH sensing and imaging detection at the levels of living cells and small animals. Finally, biomedicine applications are fully summarized, majorly involving bio-toxicity evaluation, bio-distribution, biomedical diagnosis and therapeutics. Meanwhile, the current status, challenges and perspectives are rationally commented after detailed discussions of representative and state-of-the-art studies. Overall, this present review is comprehensive, in-time and in-depth, and can facilitate the following further exploration of new and versatile DFR-MPs-pH systems toward rational design, facile preparation, superior properties, adjustable functions and highly efficient applications in promising fields.

Advances in pH Sensing: From Traditional Approaches to Next-Generation Sensors in Biological Contexts

pH has been considered one of the paramount factors in bodily functions because most cellular tasks exclusively rely on precise pH values. In this context, the current techniques for pH sensing provide us with the futuristic insight to further design therapeutic and diagnostic tools. Thus, pH-sensing (electrochemically and optically) is rapidly evolving toward exciting new applications and expanding researchers' interests in many chemical contexts, especially in biomedical applications. The adaptation of cutting-edge technology is subsequently producing the modest form of these biosensors as wearable devices, which are providing us the opportunity to target the real-time collection of vital parameters, including pH for improved healthcare systems. The motif of this review is to provide insight into trending tech-based systems employed in real-time or in-vivo pH-responsive monitoring. Herein, we briefly go through the pH regulation in the human body to help the beginners and scientific community with quick background knowledge, recent advances in the field, and pH detection in real-time biological applications. In the end, we summarize our review by providing an outlook; challenges that need to be addressed, and prospective integration of various pH in vivo platforms with modern electronics that can open new avenues of cutting-edge techniques for disease diagnostics and prevention.

Application of curcumin nanoformulations to target folic acid receptor in cancer: Recent trends and advances

Curcumin, derived from turmeric, has a strong anticancer potential known for millennia. The development of this phytochemical as a medicine has been hampered by several significant deficiencies, including its poor water solubility and low bioavailability. This review article discusses possibilities to overcome these bottlenecks by focusing on this natural polyphenol's nanoformulation. Moreover, preparation of curcumin conjugates containing folates as ligands for folic acid receptors can add a new important dimension in this field, allowing specific targeting of cancer cells, considering the significantly higher expression of these receptors in malignant tissues compared to normal cells. It is highly expected that simultaneous improvement of different aspects of curcumin in fighting against such a complex and multifaceted disease like cancer. Therefore, we can better comprehend cancer biology by developing a mechanistic understanding of curcumin, which will also inspire the scientific community to develop new pharmacological models, and exploration of emerging directions to revitalize application of natural products in cancer therapy.

Excited-state intramolecular proton transfer (ESIPT)-based fluorescent probes for biomarker detection: design, mechanism, and application

Biomarkers are essential in biology, physiology, and pharmacology; thus, their detection is of extensive importance. Fluorescent probes provide effective tools for detecting biomarkers exactly. Excited state intramolecular proton transfer (ESIPT), one of the significant photophysical processes that possesses specific photoisomerization between Keto and Enol forms, can effectively avoid annoying interference from the background with a large Stokes shift. Hence, ESIPT is an excellent choice for biomarker monitoring. Based on the ESIPT process, abundant probes were designed and synthesized using three major design methods. In this review, we conclude probes for 14 kinds of biomarkers based on ESIPT explored in the past five years, summarize these general design methods, and highlight their application for biomarker detection in vitro or in vivo.

A near-infrared probe for the real-time detection of lysosomal pH in living cells under "wash free" conditions

Lysosomal pH is an important indicator for the physiological state of eukaryotic cells. The real-time detection of intracellular lysosomal pH is critical for understanding and studying many physiological and pathological processes of cells. Herein, we designed and synthesized a series of novel pH sensors, namely W1, W2 and W3. By comparing the spectroscopic properties of the three molecules and their ability to target lysosomes in living cells, a specific probe W1 was selected for the quantitative analysis of lysosomal pH changes in live cells. W1 shows a fast, sensitive and highly selective red fluorescence response to an acidic pH value. The pK_a value of W1 is 5.84, and the fluorescence intensity ratios of I₇₄₃/I₆₈₀ under acidic conditions show a good linear relationship with the pH value. In addition, W1 shows a 100-fold difference in fluorescence from an extracellular environment to an intracellular environment, allowing it to be used as a "wash free" staining probe to visualize the pH change of lysosomes. W1 was further applied to detect the changes of lysosomal pH during apoptosis and mitophagy. Thus, W1 is expected to be a potentially useful tool for monitoring the changes of lysosomal pH in cell-related physiological or pathological states.

Probing the serum albumin binding site of fenamates and photochemical protein labeling with a fluorescent dye

Human serum albumin (HSA) can bind with numerous drugs, leading to a significant influence on drug pharmacokinetics as well as undesirable drug-drug interactions due to competitive binding. Probing the HSA drug binding site thus offers great opportunities to reveal drug-HSA binding profiles. In the present study, a fluorescent probe (E)-4-(2-(5-(4-(diphenylamino)phenyl)thiophen-2-yl)vinyl)-1-propylpyridin-1-ium (TTPy) has been prepared, which exhibits enhancement of deep-red to near-infrared (NIR) fluorescence upon HSA binding. The competitive binding assay indicated that TTPy can target the HSA binding site of fenamates, a group of non-steroidal anti-inflammatory drugs (NSAIDs), with moderate binding affinity (1.95 × 10⁶ M^-1 at 303 K). More interestingly, TTPy enables fluorescent labeling of HSA upon visible light irradiation. This study provides promising ways for HSA drug binding site identification and photochemical protein labeling.

A dual-channel chemodosimetric sensor for discrimination between hypochlorite and nerve-agent mimic DCP: application on human breast cancer cells

A styryl bridge containing a triphenylamine-thioimidazole hydrazine-based dual-analyte-responsive fluorescent sensor was designed and synthesized for the detection of the nerve gas simulant diethyl chlorophosphate (DCP) and hypochlorite (OCl^-) for the first time. Hypochlorite induces oxidative intramolecular cyclization to give a triazole structure, which exhibited blue fluorescence with excellent selectivity and a low detection limit (8.05 × 10^-7 M) in solution. Conversely, the probe forms a phosphorylated intermediate with diethyl chlorophosphate, which undergoes further hydrolyzation and presents green fluorescence in a ratiometric mode with a low detection limit (3.56 × 10^-8 M). Additionally, the as-designed sensor was utilized to construct a portable kit for real-time monitoring of DCP in a discriminatory, simple and safe manner. Lastly, the probe was also productively employed for in situ imaging of OCl^- and DCP in the living cell.