Reversible pH Response Research Articles

Highly Reversible "On-Off-On" Fluorescence Switch Governed by pH, Utilizing Bis(Benzimidazole) Derivatives with Varied Link Groups.

In this work, a series of dibenzimidazole derivatives 1-4, act as highly reversible colorimetric and fluorescent pH chemosensor, were designed and synthesized. Excellent reversible pH response of these sensors could be found by a specific pH change through obvious fluorescent color changes. The response is not affected by common cations (including Al3+, Cu2+, Ca2+, Cd2+, Co2+, Cr3+, Mg2+, Na+, K+, Ni2+, Pb2+ and Zn2+) and anions (including F-, Cl-, Br-, I-, ClO4-, H2PO4-, HSO4-, HCO3- and CH3COO-). Notably, these sensors can be reused more than 10 times without losing functionality. Unlike previous reports, the distinct properties of 1-4 are attributed to the varied link groups. Based on comprehensive experimental data and mechanistic analyses, it is concluded that sensors 1-4 are promising candidates for use as highly reversible "on-off-on" fluorescence switches under precise pH control.

Flexible polyaniline@carbon nanofiber membrane pH electrode for health care

A low-cost flexible polyaniline@carbon nanofiber membrane (PANI@CNM) electrode was fabricated by chemical in situ polymerization of aniline monomer for pH detection. The preparation condition, morphology, chemical structure and the electrochemical properties of the PANI@CNM electrode were investigated. The result showed that PANI@CNM electrode with high sensitivity of 76.2 mV/pH was prepared with 0.3 M aniline solution and hydrochloric acid as the doping acid at 0℃ for 6 h. FTIR and Raman analysis suggested that the pH sensibility of PANI is attributed to the super-Nernstian behavior of the PANI in the emerald imine form. The PANI@CNM working electrode performs a stable electrochemical property without interference by the common metal iron and biochemical, and has an outstanding reversible pH response in the pH range of 6.32–8.34 without interference of deformation. It also maintained a stable sensing performance in the temperature range of 25-40℃ for long time use and presented excellent biocompatibility. Generally, the PANI@CNM working electrode exhibits great potential in flexible biomedical and wearable pH detection application.

Strongly coupled plasmonic metal nanoparticles with reversible pH-responsiveness and highly reproducible SERS in solution.

We report a facile method to prepare polymer-grafted plasmonic metal nanoparticles (NPs) that exhibit pH-responsive surface-enhanced Raman scattering (SERS). The concept is based on the use of pH-responsive polymers, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), as multidentate ligands to wrap around the surface of NPs instead of forming polymer brushes. Upon changing the solvent quality, the grafted pH-responsive polymers would drive reversible aggregation of NPs, leading to a decreased interparticle distance. This creates numerous hot spots, resulting in a secondary enhancement of SERS as compared to the SERS from discrete NPs. For negatively charged PAA-grafted NPs, the SERS response at pH 2.5 showed a secondary enhancement of up to 104-fold as compared to the response for discrete NPs at pH 12. Similarly, positively charged PAH-grafted AuNPs showed an opposite response to pH. We demonstrated that enhanced SERS with thiol-containing and charged molecular probes was indeed from the pH-driven solubility change of polymer ligands. Our method is different from the conventional SERS sensors in the solid state. With pH-responsive polymer-grafted NPs, SERS can be performed in solution with high reproducibility and sensitivity but without the need for sample pre-concentration. These findings could pave the way for innovative designs of polymer ligands for metal NPs where polymer ligands do not compromise interparticle plasmon coupling.

Effect of UV Irradiation Time and Headgroup Interactions on the Reversible Colorimetric pH Response of Polydiacetylene Assemblies.

Polydiacetylenes are chromatic conjugated polymers formed upon the photopolymerization of self-assembled diacetylenes. They exhibit conformation-dependent colorimetric responses, usually irreversible, to external triggers. Here, we presented an approach to obtain a reversible colorimetric response to a pH change through structural modifications on the monomer and extended photopolymerization time. Both factors, enhanced hydrogen bond forming headgroups and longer UV exposure, impacted the rotational freedom of polydiacetylene conformation. Such a restricted conformation state reduced colorimetric response efficiency but enabled reversible colorimetric response to a pH change. These results highlight the possibility of obtaining a reversible colorimetric pH response of polydiacetylenes for customized sensing applications through monomer-level tailoring combined with tuning the photopolymerization time.

Chitosan/tannic acid phenamine networks-hollow mesoporous silica capsules with reversible pH response: Controlled-releasing amino acid derivatives as “green” corrosion inhibitor

A novel amino acid derivative (SM) was synthesized through Schiff base reaction between syringaldehyde (SA) and methionine (MTI), and loaded to obtain a reversible pH-responsive releasing corrosion inhibitor silica capsule (CS/TA@SM@HMSs) with chitosan/tannic acid phenamine networks on the surface. The corrosion inhibition effect of SM and CS/TA@SM@HMSs on Q235 was studied using electrochemical techniques and surface analysis. The results showed the maximum inhibition efficiency of SM reached to 93.2 % at 200ppm by immersing Q235 in 3.5 wt% NaCl solution. The theoretically calculated electron parameter (the energy gap ΔE = 4.492 eV) indicated that SM molecules were more susceptible to electron transfer with iron surfaces therefore allowing better adsorption on carbon steel surfaces to prevent corrosion. Meanwhile, UV–visible measurements showed that the chitosan/tannic acid phenamine network on the capsule surface responded to changes in pH. The reversible pH-responsive corrosion inhibitor capsule can be switched on and off several times to release SM, demonstrating reversible release and efficient corrosion protection. This study proposes a novel class of “green” amino acid derivative corrosion inhibitors, and establishes a controllable, efficient and reversible pH-responsive release system. A new approach is provided to stimulating the release of corrosion inhibitors in response to long-term corrosion protection of metals.

Macrocycle Self-Assembly Hydrogel for High-Efficient Oil-Water Separation.

Supramolecular hydrogels involved macrocycles have been explored widely in recent years, but it remains challenging to develop hydrogel based on solitary macrocycle with super gelation capability. Here, the construction of lantern[33 ]arene-based hydrogel with low critical gelation concentration (0.05 wt%), which can be used for efficient oil-water separation, is reported. The lantern[33 ]arenes self-assemble into hydrogen-bonded organic nanoribbons, which intertwine into entangled fibers to form hydrogel. This hydrogel which exhibits reversible pH-responsiveness characteristics can be coated on stainless-steel mesh by in situ sol-gel transformation. The resultant mesh exhibits excellent oil-water separation efficiency (>99%) and flux (>6 × 104 L m-2 h-1 ). This lantern[33 ]arene-based hydrogel not only sheds additional light on the gelation mechanisms for supramolecular hydrogels, but also extends the application of macrocycle-based hydrogels as functional interfacial materials.

Acid‐Triggered Aggregation of Carbon Dots Shifted Their Emission to Give Unexpected Deep‐Red Lasing

AbstractIt is challenging to realize ultra‐pH‐responsive fluorescent carbon dots (CDs), especially reversibly adjustable multichromatic emission covering a broad wavelength range including deep‐red lasing. This study reports a one‐step solvothermal treatment of pyrogallol to obtain brilliant CDs with a substantial bathochromic shift (from blue to dark red emission) induced by pH changes. The CDs show an excellent reversible pH response: simple acid treatment instantaneously shifts their initial green emission by 140 nm to a deep‐red emission with high‐color‐purity and enhances brightness, subsequent alkali addition returned the green emission, suggesting smooth and reversible regulation of fluorescence. Detailed components analyses, morphology tracking, and photodynamic studies demonstrate the discrete, reversible shift of emission derived from structural transformations, which include protonation of the CDs and their subsequent assembly and partial aggregation triggered by hydrogen bonding. The abundant H‐bonds crosslink the network of CDs, ultimately raising the quantum yield from 11.3% to 16.0%. Furthermore, the aggregated CDs crystallized into sheet‐like structures that acted as a resonant cavity for lasing show excellent gain ability and lead to strong deep‐red lasing. This study draws together pH regulation, the effects of CD's assembly, and their lasing emission to demonstrate significant potential for the development of versatile CDs.

Host-Guest Recognition Boosts Biomimetic Mono/Multivalent Cation Separation.

Biomimetic ion permselective membranes with ultrahigh ion permeability and selectivity represent a research frontier in ion separation, yet the successful fabrication of such membranes remains a formidable challenge. Here, we demonstrate a 4-sulfocalix[4]arene (4-SCA)-modified graphene oxide (GO) membrane that shows extraordinary performance in separating mono-from multivalent cations, as well as having reversible pH-responsiveness. The resulting 4-SCA-modified GO (SCA-GO) membrane preferentially transports potassium ions (K+) over radionuclide cations (Co2+, UO22+, La3+, Eu3+, and Th4+). The ion selectivities are an order of magnitude higher than that of the unmodified GO membrane. Theoretical calculations and experimental investigations demonstrate that the much-improved ion selectivity arises from the specific recognition between 4-SCA and radionuclide cations. The transport of multivalent radionuclides is impeded by a binding-obstructing mechanism from the host-guest interactions. Interestingly, the host-guest interactions are responsive to the protonation/deprotonation transformation of the 4-SCA. Therefore, the SCA-GO membrane mimics pH-regulated ion selective behavior found in biological ion channels. Our strategy of designing a biomimetic permselective GO membrane may allow efficient nuclear wastewater treatment and, more importantly, deepen our understanding of biomimetic ion transport mechanisms.

Intense pH Sensitivity Modulation in Carbon Nanotube-Based Field-Effect Transistor by Non-Covalent Polyfluorene Functionalization.

We compare the pH sensing performance of non-functionalized carbon nanotubes (CNT) field-effect transistors (p-CNTFET) and CNTFET functionalized with a conjugated polyfluorene polymer (labeled FF-UR) bearing urea-based moieties (f-CNTFET). The devices are electrolyte-gated, PMMA-passivated, 5 µm-channel FETs with unsorted, inkjet-printed single-walled CNT. In phosphate (PBS) and borate (BBS) buffer solutions, the p-CNTFETs exhibit a p-type operation while f-CNTFETs exhibit p-type behavior in BBS and ambipolarity in PBS. The sensitivity to pH is evaluated by measuring the drain current at a gate and drain voltage of -0.8 V. In PBS, p-CNTFETs show a linear, reversible pH response between pH 3 and pH 9 with a sensitivity of 26 ± 2.2%/pH unit; while f-CNTFETs have a much stronger, reversible pH response (373%/pH unit), but only over the range of pH 7 to pH 9. In BBS, both p-CNTFET and f-CNTFET show a linear pH response between pH 5 and 9, with sensitivities of 56%/pH and 96%/pH, respectively. Analysis of the I-V curves as a function of pH suggests that the increased pH sensitivity of f-CNTFET is consistent with interactions of FF-UR with phosphate ions in PBS and boric acid in BBS, with the ratio and charge of the complexed species depending on pH. The complexation affects the efficiency of electrolyte gating and the surface charge around the CNT, both of which modify the I-V response of the CNTFET, leading to the observed current sensitivity as a function of pH. The performances of p-CNTFET in PBS are comparable to the best results in the literature, while the performances of the f-CNTFET far exceed the current state-of-the-art by a factor of four in BBS and more than 10 over a limited range of pH in BBS. This is the first time that a functionalization other than carboxylate moieties has significantly improved the state-of-the-art of pH sensing with CNTFET or CNT chemistors. On the other hand, this study also highlights the challenge of transferring this performance to a real water matrix, where many different species may compete for interactions with FF-UR.

A tri-response colorimetric-fluorescent probe for pH and lysosomal imaging

Intracellular pH has been associated with multiple biological processes. However, fluorescent probes for pH are limited. Herein, a new pH fluorescent probe was developed based on reversible structural changes. This probe provided three reversible pH response modes within 2.00–12.00. Under the acidic conditions, there is no-fluorescence, under the neutral conditions, the emission is at 650 nm, under the alkaline conditions, the emissions at 650 nm decreases and at 460 nm appears and increases simultaneously. The probe solution presented distinct colors response to the pH values from 2.00 to 12.00. The fluorescent response from pH 2.00–12.00 makes the probe suitable for the monitoring pH in living cells. Moreover, the imaging results confirm that probe S can be applied in fluorescence imaging in living cells.

Multiregulated color and fluorescence of a cyanostilbene-based AIEgen by light and pH

Stimuli-responsive aggregation-induced emission (AIE) materials with regulated color and fluorescence have shown promising applications in smart optical systems, while most of them are only regulated by a single stimulus. Herein, a cyanostilbene-based fluorophore (Z-BDPA) with AIE enhancement properties is elaborately designed, which exhibits multiple regulable color and fluorescence owing to its various photochemical reactions and reversible pH response. After exposure to 420 nm light, the green emission of Z-BDPA in tetrahydrofuran (THF) becomes brighter owing to the Z→E isomerization, which can be recovered under 365 nm irradiation; the yellow fluorescence of Z-BDPA in THF/H2O mixtures with 90% water fraction (fw) becomes stronger yellow-green fluorescence due to the photodimerization. At acidic conditions, Z-BDPA powder with yellow fluorescence can become another AIEgen Z-p-BDPA with blue fluorescence via protonation, which would be recovered through deprotonation under basic conditions. Under ultraviolet light irradiation, the blue fluorescence of Z-p-BDPA is blue-shifted and increased due to the photo-isomerization and subsequent photocyclodehydrogenation reactions. Based on the regulable color and fluorescence upon the photochemical and pH responses, Z-BDPA has been successfully applied in photo-patterning and anti-counterfeiting.

Development of pH-responsive active film materials based on purple corncob and its application in meat freshness monitoring

The use of petroleum-based food packaging materials is causing environmental damage and increasing greenhouse gas production. Consequently, there is a great interest in developing smart and sustainable alternative materials. In this study, an agricultural waste product (purple corncob extract, PCCE) was used as a raw material to prepare environmentally friendly pH-sensitive packaging materials. Natural pH-sensitive pigments (anthocyanins) and lignin-containing cellulose nanocrystals (LCNC) were extracted from the purple corncobs. A cationic biopolymer (chitosan) was used as a scaffolding material to assemble the film matrix. Composite film (LCNC-PCCE-chitosan) was produced using a simple solvent casting method. Fourier transform infrared spectroscopy and scanning electron microscopy analyses showed that the PCCE and LCNC were well dispersed within the chitosan matrix and they interacted with the matrix through hydrogen bonding and electrostatic interactions. The addition of LCNC improved the hydrophobicity and mechanical properties of the film and imparted antioxidant activity and UV-blocking properties. The presence of anthocyanins in the PCCE endowed the film with a sensitive and reversible pH response, which could be well used to monitor changes in the freshness of pork and shrimp products.

Wrinkling on Stimuli-Responsive Functional Polymer Surfaces as a Promising Strategy for the Preparation of Effective Antibacterial/Antibiofouling Surfaces.

Biocompatible smart interfaces play a crucial role in biomedical or tissue engineering applications, where their ability to actively change their conformation or physico-chemical properties permits finely tuning their surface attributes. Polyelectrolytes, such as acrylic acid, are a particular type of smart polymers that present pH responsiveness. This work aims to fabricate stable hydrogel films with reversible pH responsiveness that could spontaneously form wrinkled surface patterns. For this purpose, the photosensitive reaction mixtures were deposited via spin-coating over functionalized glasses. Following vacuum, UV, or either plasma treatments, it is possible to spontaneously form wrinkles, which could increase cell adherence. The pH responsiveness of the material was evaluated, observing an abrupt variation in the film thickness as a function of the environmental pH. Moreover, the presence of the carboxylic acid functional groups at the interface was evidenced by analyzing the adsorption/desorption capacity using methylene blue as a cationic dye model. The results demonstrated that increasing the acrylic acid in the microwrinkled hydrogel effectively improved the adsorption and release capacity and the ability of the carboxylic groups to establish ionic interactions with methylene blue. Finally, the role of the acrylic acid groups and the surface topography (smooth or wrinkled) on the final antibacterial properties were investigated, demonstrating their efficacy against both gram-positive and gram-negative bacteria model strains (E. coli and S. Aureus). According to our findings, microwrinkled hydrogels presented excellent antibacterial properties improving the results obtained for planar (smooth) hydrogels.

The Construction of Stimulus‐responsive Film Electrode by the Cu‐catalyzed Radical Polymerization and its Application in Multi‐valued Biologic Systems

AbstractN‐isopropylacrylamide was polymerized on the surface of copper‐plated carbon paper electrode by a novel redox initiation system composed of persulfate and copper nanoparticles, and the PNIPAAm−Cu NPs@CP film electrode was obtained. Cyclic voltammetry (CV) results showed that the electrode exhibits a reversible temperature, pH and glucose switchable electrical signal response through the ferrocene carboxylic acid (Fc(COOH)). With this basis, a 4‐current output logic gate system consisting of 3‐response inputs of temperature, pH, and glucose was fabricated and a corresponding logic circuit for 3‐input/4‐output ports was established. This work might provide a new avenue for the development of multi‐valued biologic systems.

Protective Fabrics: Metal-Organic Framework Textiles for Rapid Photocatalytic Sulfur Mustard Simulant Detoxification

Summary Metal-organic frameworks (MOFs) can catalyze toxic chemical decontamination, but new MOF materials and synthesis strategies are needed to improve performance, particularly in field-usable MOF-textile formats. This article reports for the first time the exceptional photocatalytic reactivity of Al-PMOF (Al-porphyrin-based MOF), composed of an earth-abundant metal-containing Al(OH)O4 cluster bridged by H2TCPP (5,10,15,20-tetrakis(4-carboxyphenyl)porphyrin) chromophores, against the toxic sulfur mustard simulant 2-chloroethyl ethyl sulfide (CEES) under visible-light irradiation. Furthermore, Al-PMOF is strongly immobilized into polymeric fibers via well-controlled Al2O3 solid film conversion using dimethylformamide/water cosolvent. The approach enables a secure integration of conformal Al-PMOF films onto polymer fibers at a relatively low synthesis temperature (120°C). In addition, on a per-unit mass of MOF basis, the surface-bound Al-PMOF films enable extremely rapid CEES detoxification turnover frequency, up to 170 mol CEES mol chromophore − 1 min − 1 , more than 10-fold faster than the best MOF powders and 2-fold better than MOF films reported to date.

Co-assembly of gold nanocluster with imidazolium surfactant into ordered luminescent fibers based on aggregation induced emission strategy

Metal nanoclusters (NCs) with outstanding luminescent nature have been engineered as an emerging material, while the application of NCs in aqueous solution is subjected to major limitations because of their luminescence quenching in water. Herein, imidazolium surfactant 1-hexadecyl-3-methylimidazoliumbromide (C16mimBr) with opposite charge was used to overcome this issue based on aggregation induced emission (AIE) strategy through mild co-assembly of Au-NCs with C16mimBr. Of interest is that not only the luminescence of Au-NCs was enhanced but also fibers with strikingly regular layer-like periodic structures were obtained which is rarely prepared at room temperature. The underlying mechanism for the formation of ordered fibers was systematically investigated by a series of experiments. Firstly, the electrostatic interaction between Au-NCs and C16mimBr induces the aggregation of Au-NCs while the directional H-bonding facilitates the elongation of aggregates into 1D ordered structures. Besides, the hydrophobic interaction of alkyl chains is also crucial for the formation of fibers. Importantly, the emission of fibers exhibited reversible pH-responsiveness, i.e. when adding H+, the emission turns off meaning that the aggregates disintegrate along with fluorescence quenching. While with the addition of equal OH−, it turns on again. Such a type of optical materials with ordered structure will have potential applications in pH sensors and photoelectronic devices. It can be expected that this work will serve as a simple and low-cost platform for the preparation of ordered luminescent materials based on metal NCs.

Two-photon semiconducting polymer nanoparticles as a new platform for imaging of intracellular pH variation

Intracellular pH (pHi) plays a crucial role in cell physiological and pathological processes. We herein report an efficient pH-sensitive sensor based on two-photon excitable semiconducting polymer nanoparticles (PFV/PSMA-DA NPs) for pHi sensing. PFV/PSMA NPs were functionalized with redox-active dopamine (DA) and the obtained PFV/PSMA-DA NPs showed sensitive and reversible pH response over the pH range of 5.0–9.0. Owning to the high biocompatibility and pH-responsive DA, PFV/PSMA-DA NPs show low cytotoxicity and the quantification and imaging of intracellular pH changes of HeLa cells were successfully realized. Moreover, the detection of intracellular pH fluctuation induced by redox species such as NAC (N-acetylcysteine) and H2O2 was also achieved by both one- and two-photon excitation of the PFV/PSMA-DA NPs probe. This work clearly shows that nanoprobe based on two-photon PFV/PSMA-DA NPs could serve as a promising platform for quantitatively monitoring the intracellular pH fluctuations.

Self‐healing hydrogel of poly(vinyl alcohol)/graphite oxide with pH‐sensitive and enhanced thermal properties

ABSTRACTSupramolecular hydrogel is a fascinating polymeric material composed of three‐dimensional noncovalent networks with many outstanding properties, especially reversible relevant performances. A self‐healing supramolecular hydrogel of poly(vinyl alcohol)/graphite oxide, with reversible pH responsiveness and good thermal stability, was prepared. The morphology, functional group changes, swelling performance, thermal stability, rheological performance, and self‐healing property of the PVA/GO hydrogel were investigated. A probable mechanism between the components and potential applications were also examined in our study. The experimental results show that the PVA/GO hydrogel was not only self‐healable without external stimulus or addition of any healing agents, but also pH sensitive and with good thermal stability. Green ingredients (PVA and GO) and a simple synthesis method (a freezing/thawing treatment) may pose little threat to the environment and also promote the production of such hydrogels. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46143.

Polyethylenimine-Derived Fluorescent Nonconjugated Polymer Dots with Reversible Dual-Signal pH Response and Logic Gate Operation

A kind of nonconjugated polymer dot possessing autofluorescence was synthesized by hyperbranched polyethylenimine and salicylaldehyde via environmentally friendly imine cross-linking and self-assembly in the aqueous phase. Both fluorescence and ultraviolet–visible (UV–vis) absorption of the polymer dots showed a sensitive and reversible response to pH. The mechanism of pH-dependent optical properties was investigated. The existence of two proton-responsive functional groups (phenolic hydroxyl groups and amine groups) on the polymer dot surface is crucial. The pH-dependent fluorescence is ascribed to electron transfer, which is controlled by the protonation degree of amine groups, while the pH-dependent UV–vis absorption is induced by ionization of phenolic hydroxyl groups. Based on the pH-mediated optical properties, a colorimetric and fluorescent dual-signal pH sensor and multiple logic gates were developed. The fluorescent nonconjugated polymer dots with easy preparation and sensitive response to pH are...

PH-Responsive Polyoxometalate-Based Supramolecular Hybrid Nanomaterials and Application as Renewable Catalyst for Dyes

Keggin-type polyoxometalate (POM), phosphotungstic acid (H3PW12O40), was encapsulated by an oppositely charged COOH-functionalized surface active ionic liquid (SAIL), N-decyl-N′-carboxymethyl imidazolium bromide ([N-C10, N′-COOH-Im]Br), with the assistance of an ionic self-assembly (ISA) process in an aqueous environment. The as-prepared POM/SAIL material possesses multiple active properties, including reversible pH-response and renewable catalyst for dye degradation. Specifically, the POM-based hybrid materials show a great enhancement in catalytic efficiency when it is employed in degradation of methyl orange (MO) in aqueous solution. Furthermore, the electrostatic repulsions between POM and the deprotonated SAIL may result in the pH-induced disassembly and assembly of the hybrid nanomaterials, which provides an expedient method to regenerate the catalytic activity. Therefore, the presented POM/SAIL hybrid materials are expected to improve the common poisoning issue of the traditional heterogeneous cata...