A Julolidine Coupled Azine-based Reversible Chromo-fluorogenic Probe for Specific Detection of Cu2+ Ions.

Among the various essential trace elements for living organisms, the copper (Cu2+) ions are the most important. However, Cu2+ ions are vital for the human body and are associated with necessary physiological processes; insufficient or excessiveness has many hazardous effects on our bodies. In the present contribution, strategically, we have introduced a julolidine-coupled azine-based, 9,9'-((1E,1'E)-hydrazine-1,2-diylidene bis(methanylylidene)) bis(1,2,3,5,6,7-hexahydropyrido [3,2,1-ij] quinolin-8-ol) (HDBQ) reversible chromo-fluorogenic probe for specific detection of Cu2+ ions. Probe HDBQ exhibits observable orange colorimetric change from yellow, which is visible to the naked eye in daylight. The highly green fluorescence HDBQ becomes a non-fluorescent one with the incorporation of Cu2+ ions. Interestingly, the colorimetric change and non-fluorescent HDBQ-Cu2+ complex reverse to the original HDBQ in the presence of ethylenediamine tetraacetic acid (EDTA). The detection and quantification limit of HDBQ towards the detection of Cu2+ ions is found to be in the µM range, which is much lower than the limit (31.5 µM) recommended by WHO. We have also performed a colorimetric and fluorometric paper-based test strips-based experiment employing HDBQ for real-time on-site detection of Cu2+ ions. Using the reversibility characteristics of HDBQ for the consecutive addition of Cu2+ and EDTA, we have established the INHIBIT molecular logic gate. The present report brings a precise and sensitive probe for the detection of Cu2+ ions in real environmental and biological samples.

Spectroscopic and Density Functional Studies on the Interaction of a Naphthalene Derivative with Anions.

This article highlights the investigation of anion interactions and recognition abilities of naphthalene derivative, [(E)-1-(((4-nitrophenyl)imino)methyl)naphthalen-2-ol], (NIMO) by UV-visible spectroscopically and colorimetrically. NIMO shows selective recognition of F- ions colorimetrically, and a visual color change from yellow to pink is observed by the naked eye. The F- ions recognition is fully reversible in the presence of HSO4- ions. The limit of F- ions detection by NIMO could be possible down to 0.033 ppm-level. A paper strips-based test kit has been demonstrated to detect F- ions selectively by the naked eye, and a smartphone-based method for real sample analysis in the non-aqueous medium has also been demostrated. Spectroscopic behavior is well supported by pKa value calculation and DFT analysis, to find a correlation with receptor analyte interaction. The optical response of NIMO towards the accumulation of F- ions and, subsequently, HSO4- ions as chemical inputs provides an opportunity to construct INH and IMP molecular logic gates.

Dual-Responsive Benzo-Hemicyanine-Based Fluorescent Probe for Detection of Cyanide and Hydrogen Sulfide: Real-Time Application in Identification of Food Spoilage.

Colorimetric and fluorescent probes have received a lot of attention for detecting lethal analytes in realistic systems and in living things. Herein, a dual-approachable Benzo-hemicyaninebased red-emitting fluorescent probe PBiSMe, for distinct and instantaneous detection of CN- and HS- was synthesized. The PBiSMe emitted red fluorescence (570 nm) can switch to turn-off (570 nm) and blue fluorescence (465 nm) in response to CN- and HS-, respectively. Other nucleophilic reagents, such as reactive sulfur species (RSS) and anions, have no contact or interference with the probe; instead, a unique approach is undertaken to exclusively interact with CN- and HS- over a wide pH range. The measured detection limits for CN- (0.43 µM) and HS- (0.22 µM) ions are lower than the World Health Organization's (WHO) recommended levels in drinking water. We confirmed 1:1 stoichiometry ratio using Job's plot and observed good quantum yield for both analytes. The probe-coated paper strips were used to detect the H2S gas produced by food spoilage (such as eggs, raw meat, and fish) via an eye-catching visual response. Moreover, fluorescence bioimaging studies of living cells was done to confirm the probe's potential by monitoring the presence of CN- and HS- in a living system.

A new highly sensitive fluorescent probe for visualization of phosgene in liquid and gas phases.

Phosgene is an important and widely used highly toxic chemical that poses a serious potential threat to public health and property if leaked or abused. Therefore, developing an efficient and convenient detection method for phosgene is of great significance. In this work, we synthesized a novel fluorescent probe, BCyP, based on benzohemicyanine for highly selective and sensitive detection of phosgene in both liquid and gas phases. The probe uses amino alcohol as a specific recognition group for phosgene and does not fluoresce due to the strong intramolecular charge transfer effect (ICT). However, in the presence of phosgene, the amino alcohol part in the probe can form oxazolidinone in situ with phosgene, reducing the ICT effect in the probe molecule and lighting fluorescence, thus realizing the selective phosgene detection. The probe exhibits good specificity towards phosgene, with significant fluorescence enhancement (approximately 400-fold), a remarkable Stokes shift (139 nm), a fast response speed (less than 17 s), and a low detection limit (0.12 ppm). Additionally, we prepared a phosgene detection paper strip loaded with the probe on filter paper and combined it with color recognition software on a smartphone to achieve visual detection of phosgene in the gas phase.

Ex_g-C3N4 as a novel fluorescent probe for sensitive detecting ClO- in water samples with portable test strip.

Excessive hypochlorite (ClO-) is easy to form residues in water, which will seriously endanger human health and environmental pollution. Therefore, it is essential to develop a sensitive fluorescent sensor to detect ClO- in water. Herein, a simple and economical fluorescent probe for the detection of ClO- was designed by highly exfoliated graphite-like carbon nitride (Ex_g-C3N4). The results showed that Ex_g-C3N4 had obvious fluorescence quenching effect on ClO- with high selectivity and anti-interference ability, which was feasible for making probes for detecting ClO- in water. Sensing experiments showed that the Ex_g-C3N4 probe had the detection limit of 5.56 nM while the detection range was 0-62 mM in water. Moreover, the fast response time of Ex_g-C3N4 was less than 30 s, illustrating the superior sensitivity. Besides, the fluorescence sensing experiment was carried out in various liquid conditions, which demonstrated that Ex_g-C3N4 probe had outstanding detecting application in natural environment. A portable fluorescent test strip for rapid detecting ClO- was successfully developed. The response of the probe on test strip towards ClO- was investigated, and the detection limit (0.1 µM) is low enough to meet the safety requirements in tap water. Furthermore, the quenching mechanism of Ex_g-C3N4 probe was also discussed.

Diethylaminophenol appended pyrimidine bis hydrazone for the sequential detection of Al3+ and PPi ions.

In this study, a novel easy-to-prepare diethylaminophenol appended pyrimidine bis hydrazone (HD) has been designed and developed. The probe exhibits excellent sequential sensing characteristics towards Al3+ and PPi ions. The emission studies, various spectroscopic techniques and lifetime results have been utilized to understand the binding mechanism of HD with Al3+ ions and, to discover the specificity as well as the efficacy of the probe in sensing Al3+ ions. The good association constant in addition to the lower detection limit values makes the probe effective for the detection of Al3+. The in-situ produced HD-Al3+ ensemble could consecutively detect PPi via a turn-off fluorescence response and the selectivity and sensitivity characteristics of the generated ensemble towards PPi were described based on the demetallation approach. The overall sensing property of HD was perfectly employed for constructing logic gates, real water, and tablet applications. Paper strips, as well as cotton-swab experiments, were also conducted inorder to check the practical utility of the synthesized probe.

Reversible acidochromism of a benzoxazole based scaffold and construction of reconfigurable dual output molecular logic gates.

This report explores the reversible acidochromism of a benzoxazole-based scaffold (BPP), which is highly sensitive to the acid-base in the liquid and gas phases. With the addition of acid, the solution of BPP changes its color from yellow to pink fuchsia due to the transformation of its imine into quinonoid form. Colour change is completely reversible in the presence of the base, confirming the reversible acidochromic behavior of the present BPP system. Further, a paper strips-based test kit has been demonstrated for the practical utility of the present acidochromic BPP to identify a trace amount of acid-base in solution and gas-phase, respectively. The mechanistic aspect of detection of acid-base and colorimetric change in the presence of acid-base have been explored by density functional theoretical investigations and 1H NMR experiments. Moreover, we have constructed a reconfigurable dual-output combinatorial logic circuit by utilizing the spectral shift between two wavelengths at 404 nm and 552 nm, respectively, and colorimetric change of the BPP in the presence and absence of acid-base.

Fluorescent and Colorimetric Ionic Probe Based on Fluorescein for the Rapid and On-Site Detection of Paraquat in Vegetables and the Environment.

Detection of pesticide paraquat (PQ) is of considerable significance to ensure food safety, and its rapid and on-site detection is still a challenge. Aimed at the ion characteristics of PQ, an "enrichment and detection" strategy was proposed to improve the sensitivity through electrostatic attractions, and the ion characteristic of probes was adopted to increase the portability through avoiding aggregation-caused quenching effects in the paper strips. Herein, a novel anion-functionalized ionic liquid (IL) probe with a large conjugated plane and rich π-electrons ([Fluo][P66614]2) was designed as a fluorescent and colorimetric dual-channel probe to sensitively and rapidly detect trace amounts of PQ in vegetables and the environment. The proposed probe exhibited good linearity with a detection limit of 64.0 nM in the PQ concentration range of 0.3-7.0 µM (fluorometry) and 0.1 µM in that of 0.1-8.0 µM (colorimetry), respectively. In addition, it displayed a rapid fluorescence quenching response from green to dark (<5 s) and excellent anti-interference (among 23 other pesticides) due to dual effects of electrostatic attraction and π-π stacking. Most importantly, the lipophilic IL probe could be applied in real vegetables and environmental samples with a satisfying recovery rate of 98-103% and assembled into a handy paper strip that achieved the visual semiquantitative detection of PQ. This ionic probe provides a feasible approach for rapidly and conveniently detecting PQ for ensuring agricultural and food safety and opens a new avenue to detect ion-responsive analytes in real complex samples by an "enrichment and detection" strategy.

Colorimetric Detection of the SARS-CoV-2 Virus (COVID-19) in Artificial Saliva Using Polydiacetylene Paper Strips.

The spread and resurgence of the SARS-CoV-2 virus (COVID-19 disease) threatens human health and social relations. Prevention of COVID-19 disease partly relies on fabricating low-cost, point-of-care (POC) sensing technology that can rapidly and selectively detect the SARS-CoV-2 virus. We report a colorimetric, paper-based polydiacetylene (PDA) biosensor, designed to detect SARS-CoV-2 spike protein in artificial saliva. Analytical characterizations of the PDA sensor using NMR and FT-IR spectroscopy showed the correct structural elucidation of PCDA-NHS conjugation. The PDA sensor platform containing the N-Hydroxysuccinimide ester of 10, 12-pentacosadiynoic acid (PCDA-NHS) was divided into three experimental PCDA-NHS concentration groups of 10%, 20%, and 30% to optimize the performance of the sensor. The optimal PCDA-NHS molar concentration was determined to be 10%. The PDA sensor works by a color change from blue to red as its colorimetric output when the immobilized antibody binds to the SARS-CoV-2 spike protein in saliva samples. Our results showed that the PDA sensing platform was able to rapidly and qualitatively detect the SARS-CoV-2 spike protein within the concentration range of 1 to 100 ng/mL after four hours of incubation. Further investigation of pH and temperature showed minimal influence on the PDA sensor for the detection of COVID-19 disease. After exposure to the SARS-CoV-2 spike protein, smartphone images of the PDA sensor were used to assess the sensor output by using the red chromatic shift (RCS) of the signal response. These results indicate the potential and practical use of this PDA sensor design for the rapid, colorimetric detection of COVID-19 disease in developing countries with limited access to medical testing.

Metal-Ion-Responsive Chromogenic Probe for Rapid, On-Location Detection of Foodborne Bacterial Pathogens in Contaminated Food Items.

An amphiphilic chromogenic probe based on an oxidized di(indolyl)arylmethane backbone has been utilized for visual detection of both Cu2+ (detection limit = 8.5 ppb) and Hg2+ (detection limit = 10.2 ppb) ions via mutually independent sensing pathways. The Cu2+ ion binds to the carboxylate ends (donor site) and induces a color change from orange to yellow in the aqueous medium, while coordinating Hg2+ at the bisindolyl moiety (acceptor site) can result in the formation of a red-colored solution. Interestingly, by selecting the proper excitation channel, we can specifically excite either the monomer species or nanoaggregates. The addition of Hg2+ enhances the monomer fluorescence, while Cu2+ induces quenching. However, in both cases, metal-ion coordination triggers dissociation of a preformed self-assembled structure. Further, the in-situ-formed Cu(II) complex was utilized for rapid, on-location detection of food-borne pathogens, such as Escherichia coli (E. coli) in contaminated food items and water (detection limit = 52 CFU·mL-1). E. coli induces reduction of Cu2+ to Cu+ and transforms the yellow-colored solution into an orange-colored solution. Finally, low-cost, reusable paper strips were designed as an eco-friendly, sustainable strategy to detect bacterial pathogens.

Engaging Dynamic Surfactant Assemblies in Improving Metal Ion Sensitivity of a 1,4,7-Triazacyclononane-Based Receptor: Differential Optical Response for Cysteine and Histidine.

Self-assembly as well as metal ion binding property of an amphiphilic, dansylated 1,4,7-triazacyclononane (TACN) probe have been investigated in the presence of various surfactant assemblies in aqueous media. As expected, the receptor molecule shows highly sensitive, but rather nonspecific, interaction with metal ions in the bulk water medium. Thus, to achieve the good specificity without dampening the sensitivity of the probe, we embedded the sensor in different surfactant assemblies, such as micelles and vesicles, and explored their metal ion sensing ability. Change in microenvironment by restricting conformational mobility and increasing local hydrophobicity renders a drastic improvement in selectivity and also sensitivity toward Cu2+. Further, the preformed Cu2+ complex of the probe was utilized for exclusive "turn-on" detection of both cysteine (green fluorescence) and histidine (blue fluorescence). The diverse complexation mode of interactions with these amino acids caused a distinct change in the monomer to aggregate ratio, which was reflected in different spectral response. Furthermore, the dansylated probe was involved in developing reusable paper strips for rapid on-site detection of both Cu2+ and cysteine.

Total protein concentration and diagnostic test results for gray wolf (Canis lupus) serum using Nobuto filter paper strips.

Nobuto filter paper strips are widely used for storing blood-serum samples, but the recovery of proteins from these strips following rehydration is unknown. Poor recovery of proteins could reduce the concentration of antibodies and antigens and reduce the sensitivity of diagnostic assays. We compared the protein concentration, and its association with test sensitivity, of eluted Nobuto strip samples with paired sera. We collected and froze serum from five gray wolves (Canis lupus) for 8 mo. When thawed, we used a spectrophotometer (absorbance 280 nm) to determine the serum protein concentration for paired sera and Nobuto eluates for each animal in 2-fold serial dilutions. Total protein concentration was similar for both sample storage methods (Nobuto eluates and control sera), except for the undiluted samples in which Nobuto eluates had higher total protein concentrations. Both sample storage methods appear to produce similar results using the SNAP® 4Dx® Test to detect antibodies against pathogens causing Lyme disease, anaplasmosis, and ehrlichiosis as well as antigen for canine heartworm disease.

Filter strip as a method of choice for apoplastic fluid extraction from maize roots.

Apoplastic fluid was extracted from maize (Zea mays L.) roots using two procedures: collection from the surface of intact plant roots by filter paper strips (AF) or vacuum infiltration and/or centrifugation from excised root segments (AWF). The content of cytoplasmic marker (glucose-6-phosphate, G-6-P) and antioxidative components (enzymes, organic acids, phenolics, sugars, ROS) were compared in the extracts. The results obtained demonstrate that AF was completely free of G-6-P, as opposed to AWF where the cytoplasmic constituent was detected even at mildest centrifugation (200×g). Isoelectric focusing of POD and SOD shows the presence of cytoplasmic isoforms in AWF, and HPLC of sugars and phenolics a much more complex composition of AWF, due to cytoplasmic contamination. Organic acid composition differed in the two extracts, much higher concentrations of malic acid being registered in AF, while oxalic acid due to intracellular contamination being present only in AWF. EPR spectroscopy of DEPMPO spin trap in the extracts showed persistent generation of hydroxyl radical adduct in AF. The results obtained argue in favor of the filter strip method for the root apoplastic fluid extraction, avoiding the problems of cytoplasmic contamination and dilution and enabling concentration measurements in minute regions of the root.