Dual-Mode Optical Sensor Array for Detecting and Identifying Perillaldehyde in Solution Phase and Plant Leaf with Smartphone

An ESIPT-Based Fluorochromogenic Tweezer for Reversible and Portable Detection of Al3+ Ions

ESIPT-based fluorochromes are promising materials for the detection of various chemical and biological species, particularly metal cations. Herein, we have meticulously designed a prototypical ESIPT-based α-naphtholphthalein-derived "turn-on" fluorogenic tweezer, NPDM, for the selective detection and visualization of Al3⁺ in biological and environmental samples. NPDM was found to specifically interact with Al3⁺, exhibiting dual emissions, high sensitivity (50 s), large Stokes shifts (140 and 176 nm), and a low detection limit of 16.3 nM. Notably, the sensing mechanism of NPDM for Al3⁺ involves metal ion-coordination-induced fluorescence enhancement (CHEF), ESIPT "turn-on" effect as well as restricted intramolecular rotation (RIR). This mechanism is supported by Job's plot, high-resolution mass spectrometry (HRMS), proton nuclear magnetic resonance (¹H NMR) titrations, and density functional (DFT) calculations. Interestingly, the NPDM-Al3+ ensemble can function as a secondary chromo-fluorogenic tweezer for monitoring fluoride ions (F-) with a low detection limit of 34.8 nM. Thus, an advanced molecular memory device was constructed based on the fluorescence "off-on-off" strategy and its excellent sensing properties. Moreover, a portable, smartphone-assisted intelligent platform has been developed to facilitate in-field, cost-effective, and accurate detection of Al3⁺ in real environmental water samples. Significantly, NPDM was successfully employed to image intracellular Al3⁺ and F⁻ ions in HeLa cells without interference from oxidative stress. This represents the first reported smart molecular tweezer capable of detecting Al3⁺ ions generated during electroporation within living cells. Furthermore, the strategy developed here is valuable for the creation of novel, practically beneficial luminescent molecules and offers an advanced luminescent detection platform for point-of-care sensing of health-related ionic species.

Integrated Sensing Platform Validated for the Efficient and On-Site Screening of Amine-Containing Illicit Drugs

Efficient and reliable technologies for the on-site detection of illicit drugs are important in drug-facilitated crime investigations. However, the development of such technologies is challenging. Based on the synthetic optimization, introducing a boron ester functional group to the two furanic indicators endows the stimulus-responsive properties synergistically. The ring-opening reaction of the indicators in the presence of amine-containing illicit drugs generated well-known donor-acceptor Stenhouse adducts, accompanied by strong color changes. A small-size and lightweight laminated sensor was integrated based on the outstanding ratiometric variations of the two active furanic indicators. A prototype platform was fabricated equipped with a circuit control, a mini pump, and a signal processing system. A user-friendly detection and efficient screening of amine-containing illicit drugs, including phenethylamines, amphetamines, cathinones, and tryptamines in the liquid states were conducted. The ratiometric response of the sensor was linear in the concentration range of 2.1-10.6 μg·mL-1 for methamphetamine·HCl and methcathinone ·HCl. The detection limits for the two illicit drugs at the sublevel (ng·mL-1) were found to be 8.4 and 9.0 ng·mL-1, respectively. Double-blind field tests and different illicit drugs were evaluated with good screening capability. Successful trials showed the potential applications of the developed prototype platform for efficient and on-site analytical determination.

Fluorescent chemosensors facilitate the visualization of plant health and their living environment in sustainable agriculture

Globally, 91% of plant production encounters diverse environmental stresses that adversely affect their growth, leading to severe yield losses of 50-60%. In this case, monitoring the connection between the environment and plant health can balance population demands with environmental protection and resource distribution. Fluorescent chemosensors have shown great progress in monitoring the health and environment of plants due to their high sensitivity and biocompatibility. However, to date, no comprehensive analysis and systematic summary of fluorescent chemosensors used in monitoring the correlation between plant health and their environment have been reported. Thus, herein, we summarize the current fluorescent chemosensors ranging from their design strategies to applications in monitoring plant-environment interaction processes. First, we highlight the types of fluorescent chemosensors with design strategies to resolve the bottlenecks encountered in monitoring the health and living environment of plants. In addition, the applications of fluorescent small-molecule, nano and supramolecular chemosensors in the visualization of the health and living environment of plants are discussed. Finally, the major challenges and perspectives in this field are presented. This work will provide guidance for the design of efficient fluorescent chemosensors to monitor plant health, and then promote sustainable agricultural development.

Structure-activity relationships of aniline-based squaraines for distinguishable staining and bright two-photon fluorescence bioimaging in plant cells

An organelle-selective vision provides insights into the physiological response of plants and crops to environmental stresses in sustainable agriculture ecosystems. Biological applications often require two-photon excited fluorophores with low phototoxicity, high brightness, deep penetration, and tuneable cell entry. We obtained three aniline-based squaraines (SQs) tuned from hydrophobic to hydrophilic characteristics by modifying terminal pendant groups and substituents, and investigated their steady-state absorption and far-red-emitting fluorescence properties. The SQs exhibited two-photon absorption (2PA) ranging from 750 to 870 nm within the first biological spectral window; their structure-property relationships, corresponding to the 2PA cross sections (δ2PA), and structure differences were demonstrated. The maximum δ2PA value was ∼1220 GM at 800 nm for hydrophilic SQ3. Distinct biological staining efficiency and selective SQ bioimaging were evaluated utilizing the onion epidermal cell model. Contrary to the hydrophobic SQ1 results in the onion epidermal cell wall, amphiphilic SQ2 tagged the vacuole and nucleus and SQ3 tagged the vacuole. Distinguishable staining profiles in the roots and leaves were achieved. We believe that this study is the first to demonstrate distinct visualisation efficiency induced by the structure differences of two-photon excited SQs. Our results can help establish the versatile roles of novel near-infrared-emitting SQs in biological applications.

New 2-pyridone-based donor-acceptor dyes: the effect of the donor group position, type of π-linker and acid-base characteristics of the medium on the photophysical properties

A series of novel donor-acceptor pyrid-2-ones was synthesized. The influence of the donor group on the photophysical properties of chromophores in solution was shown by varying the methoxy group position in the electron-rich aromatic ring. The effect of the π-linker was also demonstrated by the comparison of the D-π-A pyridone with its spacer-free analogue (D-A) and with the chromophore bearing an additional thiophene bridge (D-π-π-A). It was found that the presence of a π-linker plays a crucial role in the implementation of an intramolecular charge transfer (ICT) from the donor aryl moiety to the pyridone acceptor. Thus, for the synthesized D-A, D-π-A and D-π-π-A derivatives, the photoluminescence quantum yield in DMSO solution decreases from 56.8 to 4.3 and 3.5%, respectively, along with a strong bathochromic shift both for absorption (66 nm) and emission (162 nm) bands. Also, the possibility of shifting the equilibrium in DMSO solution towards either the pyridone form or the anionic form by the addition of a strong acid (TFA) and base (DBN) respectively was shown. Drastic changes in the photoluminescence of the solutions showed prospects for the application of the synthesized donor-acceptor pyridone derivatives as naked-eye acid-base indicators in organic media.