Optical Sensing and Imaging of pH Values: Spectroscopies, Materials, and Applications

Synthesis of rhenium disulfide nanodots exhibiting pH-dependent fluorescence and phosphorescence for anticounterfeiting and hazardous gas detection

The synthesis and characterization of ReS2 nanodots (NDs) are detailed, by highlighting their structure, morphological, and optical properties. ReS2 NDs were synthesized using NH4ReO4 as a rhenium source, thiourea as a sulfur source, and N-acetyl cysteine as a capping agent. The synthesis involved the hydrothermal reaction of these precursors, leading to the nucleation and growth of ReS2 NDs. Characterization techniques including transmission electron microscopy, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy confirmed the formation of ReS2 NDs with a spherical morphology, crystalline structure, and rich sulfur sites. The fluorescence behavior of ReS2 NDs was found to be influenced by the solution pH, with fluorescence intensity increasing with rising pH values. This pH-dependent fluorescence response was attributed to the dissociation of functional groups and the subsequent impact on the excited-state proton transfer process. The fluorescence intensity of ReS2 NDs showed a correlation with solution pH, enabling pH detection from 3.0 to 12.5 with an interval of 0.5 pH unit. Additionally, the incorporation of ReS2 NDs into a polyvinyl alcohol (PVA) matrix resulted in pH-sensitive phosphorescence, offering a new avenue for pH sensing. The strong interaction between PVA and ReS2 NDs was proposed to enhance phosphorescence intensity and trigger a blue shift in the phosphorescent peak at high pH. The ReS2 NDs/PVA-deposited filter paper exhibited pH-sensitive fluorescence and phosphorescence, which could be utilized as unique identifiers or authentication markers. Moreover, the ReS2 NDs/PVA-deposited filter paper showed potential for discriminating between hydrogen chloride and ammonia, based on their distinct fluorescence and phosphorescence responses.

Optimization of a tunable process for rapid production of calcium phosphate microparticles using a droplet-based microfluidic platform

Calcium phosphate (CaP) biomaterials are amongst the most widely used synthetic bone graft substitutes, owing to their chemical similarities to the mineral part of bone matrix and off-the-shelf availability. However, their ability to regenerate bone in critical-sized bone defects has remained inferior to the gold standard autologous bone. Hence, there is a need for methods that can be employed to efficiently produce CaPs with different properties, enabling the screening and consequent fine-tuning of the properties of CaPs towards effective bone regeneration. To this end, we propose the use of droplet microfluidics for rapid production of a variety of CaP microparticles. Particularly, this study aims to optimize the steps of a droplet microfluidic-based production process, including droplet generation, in-droplet CaP synthesis, purification and sintering, in order to obtain a library of CaP microparticles with fine-tuned properties. The results showed that size-controlled, monodisperse water-in-oil microdroplets containing calcium- and phosphate-rich solutions can be produced using a flow-focusing droplet-generator microfluidic chip. We optimized synthesis protocols based on in-droplet mineralization to obtain a range of CaP microparticles without and with inorganic additives. This was achieved by adjusting synthesis parameters, such as precursor concentration, pH value, and aging time, and applying heat treatment. In addition, our results indicated that the synthesis and fabrication parameters of CaPs in this method can alter the microstructure and the degradation behavior of CaPs. Overall, the results highlight the potential of the droplet microfluidic platform for engineering CaP microparticle biomaterials with fine-tuned properties.

Highly sensitive fiber-optic chemical pH sensor based on surface modification of optical fiber with ZnCdSe/ZnS quantum dots

The pH value plays a vital role in many biological and chemical reactions. In this work, the fiber-optic chemical pH sensors were fabricated based on carboxyl ZnCdSe/ZnS quantum dots (QDs) and tapered optical fiber. The photoluminescence (PL) intensity of QDs is pH-dependence because protonation and deprotonation can affect the process of electron-hole recombination. The evanescent wave of tapered optical fiber was used as excitation source in the process of PL. To obtain higher sensitivity, the end faces of fiber were optimized for cone region. By lengthening the cone region and shrinking the end diameter of optical fiber, evanescent wave was enhanced and the excitation times of QDs were increased, which improved the PL intensity and the sensitivity of the sensor. The sensitivity of sensor can reach as high as 0.139/pH in the range of pH 6.00-9.01. The surface functional modification was adopted to prepare sensing films. The carboxyl groups on the QDs ligands are chemically bonded to the fiber surface, which is good for response time (40 s) and stability (decreased 0.9 % for 5 min). These results demonstrated that ZnCdSe/ZnS QDs-based fiber-optic chemical pH sensors are promising approach in rapid and precise pH detection.

Tunable Self-Referenced Molecular Thermometers via Manipulation of Dual Emission in Platinum(II) Pyridinedipyrrolide Complexes

Optical temperature sensors based on self-referenced readout schemes such as the emission ratio and the decay time are crucial for a wide range of applications, with the former often preferred due to simplicity of instrumentation. This work describes a new group of dually emitting dyes, platinum(II) pincer complexes, that can be used directly for ratiometric temperature sensing without an additional reference material. They consist of Pt(II) metal center surrounded by a pyridinedipyrrolide ligand (PDP) and a terminal ligand (benzonitrile, pyridine, 1-butylimidazol or carbon monoxide). Upon excitation with blue light, these complexes exhibit green to orange emission, with quantum yields in anoxic toluene at 25 °C ranging from 13% to 86% and decay times spanning from 8.5 to 97 μs. The emission is attributed to simultaneous thermally activated delayed fluorescence (TADF) and phosphorescence processes on the basis of photophysical investigations and DFT calculations. Rather uniquely, simple manipulations in substituents of the PDP ligand and alteration of the terminal ligand allow fine-tuning of the ratio between TADF and phosphorescence from almost 100% TADF emission (Pt(MesPDPC6F5(BN)) to over 80% of phosphorescence (Pt(PhPDPPh(BuIm)). Apart from ratiometric capabilities, the complexes also are useful as decay time-based temperature indicators with temperature coefficients exceeding 1.5% K-1 in most cases. Immobilization of the dyes into oxygen-impermeable polyacrylonitrile produces temperature sensing materials that can be read out with an ordinary RGB camera or a smartphone. In addition, Pt(PhPDPPh)Py can be incorporated into biocompatible RL100 nanoparticles suitable for cellular nanothermometry, as we demonstrate with temperature measurements in multicellular colon cancer spheroids.

Optical pH Sensor Based on a Long-Period Fiber Grating Coated with a Polymeric Layer-by-Layer Electrostatic Self-Assembled Nanofilm

An optical fiber pH sensor based on a long-period fiber grating (LPFG) is reported. Two oppositely charged polymers, polyethylenimine (PEI) and polyacrylic acid (PAA), were alternately deposited on the sensing structure through a layer-by-layer (LbL) electrostatic self-assembly technique. Since the polymers are pH sensitive, their refractive index (RI) varies when the pH of the solution changes due to swelling/deswelling phenomena. The fabricated multilayer coating retained a similar property, enabling its use in pH-sensing applications. The pH of the PAA dipping solution was tuned so that a coated LPFG achieved a pH sensitivity of (6.3 ± 0.2) nm/pH in the 5.92-9.23 pH range. Only two bilayers of PEI/PAA were used as an overlay, which reduces the fabrication time and increases the reproducibility of the sensor, and its reversibility and repeatability were demonstrated by tracking the resonance band position throughout multiple cycles between different pH solutions. With simulation work and experimental results from a low-finesse Fabry-Perot (FP) cavity on a fiber tip, the coating properties were estimated. When saturated at low pH, it has a thickness of 200 nm and 1.53 ± 0.01 RI, expanding up to 310 nm with a 1.35 ± 0.01 RI at higher pH values, mostly due to the structural changes in the PAA.

Cy5 Dye Cassettes Exhibit Through-Bond Energy Transfer and Enable Ratiometric Fluorescence Sensing

The chemosensor literature contains many reports of fluorescence sensing using polyaromatic hydrocarbon fluorophores such as pyrene, tetraphenylethylene, or polyaryl(ethynylene), where the fluorophore is excited with ultraviolet light (<400 nm) and emits in the visible region of 400-500 nm. There is a need for general methods that convert these "turn-on" hydrocarbon fluorescent sensors into ratiometric sensing paradigms. One simple strategy is to mix the responsive hydrocarbon sensor with a second non-responsive dye that is excited by ultraviolet light but emits at a distinctly longer wavelength and thus acts as a reference signal. Five new cyanine dye cassettes were created by covalently attaching a pyrene, tetraphenylethylene, or biphenyl(ethynylene) component as the ultraviolet-absorbing energy donor directly to the pentamethine chain of a deep-red cyanine (Cy5) energy acceptor. Fluorescence emission studies showed that these Cy5-cassettes exhibited large pseudo-Stokes shifts and high through-bond energy transfer efficiencies upon excitation with ultraviolet light. Practical potential was demonstrated with two examples of ratiometric fluorescence sensing using a single ultraviolet excitation wavelength. One example mixed a Cy5-cassette with a pyrene-based fluorescent indicator that responded to changes in Cu2+ concentration, and the other example mixed a Cy5-cassette with the fluorescent pH sensing dye, pyranine.

On-Demand Optimization of Colorimetric Gas Sensors Using a Knowledge-Aware Algorithm-Driven Robotic Experimental Platform

Synthesizing the best material globally is challenging; it needs to know what and how much the best ingredient composition should be for satisfying multiple figures of merit simultaneously. Traditional one-variable-at-a-time methods are inefficient; the design-build-test-learn (DBTL) method could achieve the optimal composition from only a handful of ingredients. A vast design space needs to be explored to discover the possible global optimal composition for on-demand materials synthesis. This research developed a hypothesis-guided DBTL (H-DBTL) method combined with robots to expand the dimensions of the search space, thereby achieving a better global optimal performance. First, this study engineered the search space with knowledge-aware chemical descriptors and customized multiobjective functions to fulfill on-demand research objectives. To verify this concept, this novel method was used to optimize colorimetric ammonia sensors across a vast design space of as high as 19 variables, achieving two remarkable optimization goals within 1 week: first, a sensing array was developed for ammonia quantification of a wide dynamic range, from 0.5 to 500 ppm; second, a new state-of-the-art detection limit of 50 ppb was reached. This work demonstrates that the H-DBTL approach, combined with a robot, develops a novel paradigm for the on-demand optimization of functional materials.

Albumin Hydrogel-Coated Mesoporous Silica Nanoparticle as a Carrier of Cationic Porphyrin and Ratiometric Fluorescence pH Sensor

Here, we report that a mesoporous silica nanoparticle (MSN) coated with a fluoresceine-labeled bovine serum albumin (F-BSA) hydrogel layer works as a temperature-responsive nanocarrier for tetrakis-N-methylpyridyl porphyrin (TMPyP) and as a fluorescence ratiometric pH probe. F-BSA hydrogel-coated MSN containing TMPyP (F-BSA/MSN/TMPyP) was synthesized by thermal gelation of denatured F-BSA on the external surface of MSN. The F-BSA hydrogel layer was composed of an inner hard corona layer and an outer soft layer and was stable under physiological conditions. F-BSA/MSN/TMPyP exhibited temperature-dependent exponential release of TMPyP. In this release profile, the MSN was found to be a suitable host for stable encapsulation of tetracationic TMPyP by electrostatic interactions, and the F-BSA hydrogel layer mediated the diffusion of TMPyP from the MSN pore interior into the solution phase. Increasing temperature promoted partitioning of TMPyP from the pore interior to the F-BSA hydrogel layer, from where it was spontaneously released into the bulk solution phase by cation exchange. F-BSA/MSN/TMPyP also gave a linear ratiometric fluorescence response (1.3 per pH unit) in the pH range from 6.1 to 8.9.

Real-time visualization the pH fluctuations of living cells with a ratiometric near-infrared fluorescent probe

In situ real-time quantitative monitoring pH fluctuation in complex living systems is vitally significant. In the current work, a ratiometric near-infrared (NIR) probe (MCyOH) was developed to confront this challenge. MCyOH exhibited good sensitivity, photostability, reversibility, and an ideal pKa (pKa = 6.65). Ratiometric character of MCyOH is beneficial to accuracy detect the pH fluctuations in living cells under different stimulation. The observations showed that intracellular pH was decreased when HepG2 cells under oxidative stress or starvation conditions. In particular, HepG2 cells was acidulated after addition of ethanol, however, the acidification phenomenon was attenuated or disappeared when HepG2 cells preincubated with disulfiram or fomepizole. Finally, MCyOH was successfully applied to observe the increasement of intracellular pH when HepG2 cells treated with fomepizole individually. Overall, MCyOH would be a practical candidate to explore pH-associated physiological and pathological varieties.

Biodegradable, Biocompatible, and Implantable Multifunctional Sensing Platform for Cardiac Monitoring

Cardiac monitoring after heart surgeries is crucial for health maintenance and detecting postoperative complications early. However, current methods like rigid implants have limitations, as they require performing second complex surgeries for removal, increasing infection and inflammation risks, thus prompting research for improved sensing monitoring technologies. Herein, we introduce a nanosensor platform that is biodegradable, biocompatible, and integrated with multifunctions, suitable for use as implants for cardiac monitoring. The device has two electrochemical biosensors for sensing lactic acid and pH as well as a pressure sensor and a chemiresistor array for detecting volatile organic compounds. Its biocompatibility with myocytes has been tested in vitro, and its biodegradability and sensing function have been proven with ex vivo experiments using a three-dimensional (3D)-printed heart model and 3D-printed cardiac tissue patches. Moreover, an artificial intelligence-based predictive model was designed to fuse sensor data for more precise health assessment, making it a suitable candidate for clinical use. This sensing platform promises impactful applications in the realm of cardiac patient care, laying the foundation for advanced life-saving developments.

Applications of inverse opal photonic crystal hydrogels in the preparation of acid-base color-changing materials

Hydrogels are three-dimensional (3D) crosslinked network hydrophilic polymers that have structures similar to that of biological protein tissue and can quickly absorb a large amount of water. Opal photonic crystals (OPCs) are a kind of photonic band gap material formed by the periodic arrangement of 3D media, and inverse opal photonic crystals (IOPCs) are their inverse structure. Inverse opal photonic crystal hydrogels (IOPCHs) can produce corresponding visual color responses to a change in acid or alkali in an external humid environment, which has wide applications in chemical sensing, anti-counterfeiting, medical detection, intelligent display, and other fields, and the field has developed rapidly in recent years. In this paper, the research progress on fast acid-base response IOPCHs (pH-IOPCHs) is comprehensively described from the perspective of material synthesis. The technical bottleneck of enhancing the performance of acid-base-responsive IOPCHs and the current practical application limitations are summarized, and the development prospects of acid-base-responsive IOPCHs are described. These comprehensive analyses are expected to provide new ideas for solving problems in the preparation and application of pH-IOPCHs.

Next-generation of smart dressings: Integrating multiplexed sensors and theranostic functions

Non-healing wounds represent a significant burden for healthcare systems and society, giving rise to severe economic and human issues. Currently, the use of dressings and visual assessment represent the primary and standard care for wounds. Conventional dressings, like cotton gauze, provide only passive physical protection. Besides, they end up paradoxically hampering the wound-healing process by producing tissue damage and pain when removed during routine check-ups. In response to these limitations, researchers, engineers, and technologists are developing innovative dressings that incorporate advanced diagnostic and therapeutic functionalities, coined as "smart dressings". Now, the maturation of smart dressing is bringing them closer to real-life applications, leading to an exciting new generation of these devices. The next generation of smart dressings is capable of monitoring in real-time multiple biomarkers while including pro-healing capabilities in a single platform. Such multiplexed and theranostic smart dressings are expected to offer a timely biomarker-directed diagnosis of non-healing wounds while enabling rapid, automated, and personalized treatments of infection and chronicity. Herein, we provide an insightful overview of these advantageous devices, delving into the diverse spectrum of possible engineering strategies. This encompasses the use of electrochemical and optical platforms with diverse multiplexing architectures, such as multi-zone sensing arrays and multi-layered devices. Open or closed-loop theranostic mechanisms using various stimuli-responsive materials that could be internally or externally controlled are also included. Finally, a critical discussion on the main challenges and future directions of smart dressings is also offered.

Ratiometric fluorescent sensor with large pseudo-Stokes shifts for precise sensing and imaging of pH without interferential background fluorescence

Endowing fluorescent pH sensors with large Stokes shifts promises to resolve interferential background fluorescence in practice, and yet few such method has been reported, owing to lack of luminescent materials with large Stokes shifts used in fluorescent sensors. Herein, we elaborately designed NaGdF4:Ce@NaGdF4:Nd@NaYF4:Eu core-double shells (CDS) lanthanide-doped fluoride nanoparticles (LFNPs), employing Gd3+-mediated energy migration and interfacial energy transfer to realize intense red and NIR emissions under 254 nm irradiation, and pseudo-Stokes shifts of which reached up to striking 361 nm and 610 nm, respectively. The CDS LFNPs collaborated with absorption-based pH indicator bromocresol green to from a novel fluorescent sensor film, and employing low-cost dual chip RGB-NIR camera to precisely record luminescence signals. On the basis of inner-filter effects, this senor system enabled accurate ratiometric read-out of pH value ranging from 5 to 6 (pKa ± 0.5), according to intensity ratios of pH-sensitive red emissions and referenced NIR emissions, avoiding common errors (e.g., fluctuant light sources). Notably, the large pseudo-Stokes shifts allowed red and NIR emissions far from the interfering background fluorescence possessing relatively small Stokes shifts, ensuring elevated signal-to-noise ratio and accurate pH determination. Therefore, the devised pH sensor system based on the CDS LFNPs exhibited sufficient accuracy in autofluorescent real samples (e.g., algae, serum), revealing a novel way of employing large pseudo-Stokes shifts to realize the background-free pH measurement and 2D imaging.

Negative Capacitance Dual-Gated ISFETs as Ultra-Sensitive pH Sensors

Ion-sensitive field-effect transistors (ISFETs) are promising candidates for next-generation pH sensors, enabling highly sensitive and label-free biomolecular and chemical detection. Emerging FETs based on the negative capacitance (NC) effect offer steep-subthreshold switching and higher drive current simply by integrating a ferroelectric (FE) material into the gate stack. Here, we propose a novel NC dual-gated ISFET (NC-DG-ISFET)-based pH sensor, with FE layers integrated into both the top and the bottom gate stacks. The current and voltage sensitivities of the proposed device are extracted from its transfer characteristics, obtained by combining the numerical solutions of the one-dimensional (1D) Landau-Khalatnikov (L-K) equation with three-dimensional (3D) technology computer-aided design (TCAD) simulations. Results show that the NC-DG-ISFET can surpass the sensitivity of some of the state-of-the-art DG-ISFET pH sensors. The inclusion of the FE layers into the gate stacks of a baseline DG-ISFET leads to 51% reduction in subthreshold swing (SS), causing a 5× increase in current sensitivity (SI) in the subthreshold region of operation and a 2× increase in voltage sensitivity (SV). The influence of channel thickness and channel length on the sensor performance is also invesitgated. The findings presented here provide a new pathway to leverage the steep-switching behavior of NCFETs for the next generation of highly sensitive and label-free DG-ISFET pH sensors.

Optical sensors (optodes) for multiparameter chemical imaging: classification, challenges, and prospects

Chemical gradients and uneven distribution of analytes are common in natural and artificial systems. As a result, the ability to visualize chemical distributions in two or more dimensions has gained significant importance in recent years. This has led to the integration of chemical imaging techniques into all domains of analytical chemistry. In this review, we focus on the use of optical sensors, so-called optodes, to obtain real-time and multidimensional images of two or more parameters simultaneously. It is important to emphasize that multiparameter imaging in this context is not confined solely to multiple chemical parameters (analytes) but also encompasses physical (e.g., temperature or flow) or biological (e.g., metabolic activity) parameters. First, we discuss the technological milestones that have paved the way for chemical imaging using optodes. Later, we delve into various strategies that can be taken to enable multiparameter imaging. The latter spans from developing novel receptors that enable the recognition of multiple parameters to chemometrics and machine learning-based techniques for data analysis. We also explore ongoing trends, challenges, and prospects for future developments in this field. Optode-based multiparameter imaging is a rapidly expanding field that is being fueled by cutting-edge technologies. Chemical imaging possesses the potential to provide novel insights into complex samples, bridging not only across various scientific disciplines but also between research and society.

A tuning fork-shaped bisbenzothiazole derivative as a pH-responsive digital fluorescent probe and its ex vivo evaluation

A new highly emissive pH-responsive near-IR active digital probe was designed and synthesized. The probe is based on a bisbenzothiazole motif with a highly vulnerable hydrogen unit attached in an intramolecular fashion. The probe produced a large Stokes shift which was observed to be highly pH dependent. The optical pH dependence can be used for sensing pH over a wide range.

The Good pH probe: non-invasive pH in-line monitoring using Good buffers and Raman spectroscopy

In bioprocesses, the pH value is a critical process parameter that requires monitoring and control. For pH monitoring, potentiometric methods such as pH electrodes are state of the art. However, they are invasive and show measurement value drift. Spectroscopic pH monitoring is a non-invasive alternative to potentiometric methods avoiding this measurement value drift. In this study, we developed the Good pH probe, which is an approach for spectroscopic pH monitoring in bioprocesses with an effective working range between pH 6 and pH 8 that does not require the estimation of activity coefficients. The Good pH probe combines for the first time the Good buffer 3-(N-morpholino)propanesulfonic acid (MOPS) as pH indicator with Raman spectroscopy as spectroscopic technique, and Indirect Hard Modeling (IHM) for the spectral evaluation. During a detailed characterization, we proved that the Good pH probe is reversible, exhibits no temperature dependence between 15 and 40 °C, has low sensitivity to the ionic strength up to 1100 mM, and is applicable in more complex systems, in which other components significantly superimpose the spectral features of MOPS. Finally, the Good pH probe was successfully used for non-invasive pH in-line monitoring during an industrially relevant enzyme-catalyzed reaction with a root mean square error of prediction (RMSEP) of 0.04 pH levels. Thus, the Good pH probe extends the list of critical process parameters monitorable using Raman spectroscopy and IHM by the pH value.

Low-Cost Optical pH Sensor with a Polyaniline (PANI)-Sensitive Layer Based on Commercial Off-the-Shelf (COTS) Components

In this paper, we presented a novel, compact, conceptually simple, and fully functional low-cost prototype of a pH sensor with a PANI thin film as a sensing layer. The PANI deposition process is truly low-cost; it performs from the liquid phase, does not required any specialized equipment, and comprises few processing steps. The resulting PANI layer has excellent stability, resistance to solvents, and bio- and chemical compatibility. The pH sensor's sensing part includes only a few components such as a red-light-emitting diode (LED) as a light source, and a corresponding photodiode (PD) as a detector. Unlike other PANI-based sensors, it requires no sophisticated and expensive techniques and components such lasers to excite the PANI or spectrometry to identify the PANI color change induced by pH variation. The pH sensor is sensitive in the broad pH range of 3 to 9, which is useful for numerous practical applications. The sensor requires a tiny volume of the test specimen, as little as 55 µL. We developed a fully integrated packaging solution for the pH sensor that comprises a limited number of components. The pH sensor comprises exclusively commercial off-the-shelf (COTS) components and standard printed circuit boards. The pH sensor is assembled using standard surface mounting technology (SMT).

Oligohexamethylene Guanidine Derivative as a Means to Prevent Biological Fouling of a Polymer-Based Composite Optical Oxygen Sensor

The use of biocidal agents is a common practice for protection against biofouling in biomass-rich environments. In this paper, oligohexamethyleneguanidine (OHMG) polymer, known for its biocidal properties, was further modified with para-aminosalicylic acid (PAS) to enhance its properties against microorganisms coated with a lipid membrane. The structure of the product was confirmed by 1H NMR, 13C NMR, and FTIR spectroscopy. The values of the minimum inhibitory concentration (MIC) against Mycobacterium smegmatis ATCC 607 and Pseudomonas chlororaphis 449 were found to be 1.40 and 1.05 μg/mL, respectively. The synthesized substance was used as an additive to the polymer matrix of the composite optical oxygen sensor material. A series of samples with different contents of OHMG-PAS was prepared using a co-dissolution method implying the fabrication of a coating from a solution containing both polymers. It turned out that the mutual influence of the components significantly affects the distribution of the indicator in the matrix, surface morphology, and contact angle. The optimal polymer content turned out to be wt.3%, at which point the water contact angle reaches almost 122°, and the fouling rate decreases by almost five times, which is confirmed by both the respiratory MTT assay and confocal microscopy with staining. This opens up prospects for creating stable and biofouling-resistant sensor elements for use in air tanks or seawater.

Smart Wearable Nanopaper Patch for Continuous Multiplexed Optical Monitoring of Sweat Parameters

Notwithstanding the substantial progress in optical wearable sensing devices, developing wearable optical sensors for simultaneous, real-time, and continuous monitoring of multiple biomarkers is still an important, yet unmet, demand. Aiming to address this need, we introduced for the first time a smart wearable optical sensor (SWOS) platform combining a multiplexed sweat sensor sticker with its IoT-enabled readout module. We employed our SWOS system for on-body continuous, real-time, and simultaneous fluorimetric monitoring of sweat volume (physical parameter) and pH (chemical marker). Herein, a variation in moisture (5-45 μL) or pH (4.0-7.0) causes a color/fluorescence change in the copper chloride/fluorescein immobilized within a transparent chitin nanopaper (ChNP) in a selective and reversible manner. Human experiments conducted on athletic volunteers during exercise confirm that our developed SWOS platform can be efficiently exploited for smart perspiration analysis toward personalized health monitoring. Moreover, our system can be further extended for the continuous and real-time multiplexed monitoring of various biomarkers (metabolites, proteins, or drugs) of sweat or other biofluids (for example, analyzing exhaled breath by integrating onto a facemask).

pH biosensors based on hydrogel optical fiber

This paper presents a hydrogel optical fiber fluorescence pH sensor doped with 5(6)-carboxyfluorescein (5(6)-FAM). The hydrogel optical fiber was fabricated with 2-hydroxy-2-methylpropiophenone as a photoinitiator, with different concentrations of polyethylene glycol diacrylate (PEGDA) for the core and cladding. A pH-sensitive fluorescence indicator 5(6)-FAM was doped into the core of the fiber. The prepared hydrogel optical fiber pH sensor showed good response within the pH range of 5.0-9.0. The linear range of the pH sensor is 6.0 to 8.0, with R 2=0.9904; within this range, the sensor shows good repeatability and reversibility, and the resolution is 0.07 pH units. The pHs of pork tissues soaked in different pH buffers were detected by the hydrogel optical fiber pH sensor; the linearity is 0.9828 when the pork tissue pH is in the range of 6.0-7.5. Due to the good ion permeability and biocompatibility of the hydrogel, this hydrogel optical fiber pH sensor is expected to be used in biomedical applications.

Current and future technologies for monitoring cultured meat: A review

The high population growth rate, massive animal food consumption, fast economic progress, and limited food resources could lead to a food crisis in the future. There is a huge requirement for dietary proteins including cultured meat is being progressed to fulfill the need for meat-derived proteins in the diet. However, production of cultured meat requires monitoring numerous bioprocess parameters. This review presents a comprehensive overview of various widely adopted techniques (optical, spectroscopic, electrochemical, capacitive, FETs, resistive, microscopy, and ultrasound) for monitoring physical, chemical, and biological parameters that can improve the bioprocess control in cultured meat. The methods, operating principle, merits/demerits, and the main open challenges are reviewed with the aim to support the readers in advancing knowledge on novel sensing systems for cultured meat applications.

Dual-Lifetime Referencing (t-DLR) Optical Fiber Fluorescent pH Sensor for Microenvironments

The pH behavior in the μm to cm thick diffusion boundary layer (DBL) surrounding many aquatic species is dependent on light-controlled metabolic activities. This DBL microenvironment exhibits different pH behavior to bulk seawater, which can reduce the exposure of calcifying species to ocean acidification conditions. A low-cost time-domain dual-lifetime referencing (t-DLR) interrogation system and an optical fiber fluorescent pH sensor were developed for pH measurements in the DBL interface. The pH sensor utilized dual-layer sol-gel coatings of pH-sensitive iminocoumarin and pH-insensitive Ru(dpp)3-PAN. The sensor has a dynamic range of 7.41 (±0.20) to 9.42 ± 0.23 pH units (95% CI, T = 20 °C, S = 35), a response time (t90) of 29 to 100 s, and minimal salinity dependency. The pH sensor has a precision of approximately 0.02 pHT units, which meets the Global Ocean Acidification Observing Network (GOA-ON) "weather" measurement quality guideline. The suitability of the t-DLR optical fiber pH sensor was demonstrated through real-time measurements in the DBL of green seaweed Ulva sp. This research highlights the practicability of optical fiber pH sensors by demonstrating real-time pH measurements of metabolic-induced pH changes.

Acid/Base-Triggered Photophysical and Chiroptical Switching in a Series of Helicenoid Compounds

A series of molecules that possess two quinolines, benzoquinolines, or phenanthrolines connected in a chiral fashion by a biaryl junction along with their water-soluble derivatives was developed and characterized. The influence of the structure on the basicity of the nitrogen atoms in two heterocycles was examined and the photophysical and chiroptical switching activity of the compounds upon protonation was studied both experimentally and computationally. The results demonstrated that changes in the electronic structure of the protonated vs. neutral species, promoting a bathochromic shift of dominant electronic transitions and alternation of their character from π-to-π* to charge-transfer-type, when additionally accompanied by the high structural flexibility of a system, leading to changes in conformational preferences upon proton binding, produce particularly pronounced modifications of the spectral properties in acidic medium. The latter combined with reversibility of the read-out make some of the molecules in this series very promising multifunctional pH probes.

Ionic liquids revolutionizing biomedicine: recent advances and emerging opportunities

Ionic liquids (ILs), due to their inherent structural tunability, outstanding miscibility behavior, and excellent electrochemical properties, have attracted significant research attention in the biomedical field. As the application of ILs in biomedicine is a rapidly emerging field, there is still a need for systematic analyses and summaries to further advance their development. This review presents a comprehensive survey on the utilization of ILs in the biomedical field. It specifically emphasizes the diverse structures and properties of ILs with their relevance in various biomedical applications. Subsequently, we summarize the mechanisms of ILs as potential drug candidates, exploring their effects on various organisms ranging from cell membranes to organelles, proteins, and nucleic acids. Furthermore, the application of ILs as extractants and catalysts in pharmaceutical engineering is introduced. In addition, we thoroughly review and analyze the applications of ILs in disease diagnosis and delivery systems. By offering an extensive analysis of recent research, our objective is to inspire new ideas and pathways for the design of innovative biomedical technologies based on ILs.

Probing organoid metabolism using fluorescence lifetime imaging microscopy (FLIM): The next frontier of drug discovery and disease understanding

Organoid models have been used to address important questions in developmental and cancer biology, tissue repair, advanced modelling of disease and therapies, among other bioengineering applications. Such 3D microenvironmental models can investigate the regulation of cell metabolism, and provide key insights into the mechanisms at the basis of cell growth, differentiation, communication, interactions with the environment and cell death. Their accessibility and complexity, based on 3D spatial and temporal heterogeneity, make organoids suitable for the application of novel, dynamic imaging microscopy methods, such as fluorescence lifetime imaging microscopy (FLIM) and related decay time-assessing readouts. Several biomarkers and assays have been proposed to study cell metabolism by FLIM in various organoid models. Herein, we present an expert-opinion discussion on the principles of FLIM and PLIM, instrumentation and data collection and analysis protocols, and general and emerging biosensor-based approaches, to highlight the pioneering work being performed in this field.

Recent Development of Polymer Nanofibers in the Field of Optical Sensing

In recent years, owing to the continuous development of polymer nanofiber manufacturing technology, various nanofibers with different structural characteristics have emerged, allowing their application in the field of sensing to continually expand. Integrating polymer nanofibers with optical sensors takes advantage of the high sensitivity, fast response, and strong immunity to electromagnetic interference of optical sensors, enabling widespread use in biomedical science, environmental monitoring, food safety, and other fields. This paper summarizes the research progress of polymer nanofibers in optical sensors, classifies and analyzes polymer nanofiber optical sensors according to different functions (fluorescence, Raman, polarization, surface plasmon resonance, and photoelectrochemistry), and introduces the principles, structures, and properties of each type of sensor and application examples in different fields. This paper also looks forward to the future development directions and challenges of polymer nanofiber optical sensors, and provides a reference for in-depth research of sensors and industrial applications of polymer nanofibers.

Fluorescent nano- and microparticles for sensing cellular microenvironment: past, present and future applications

The tumor microenvironment (TME) demonstrates distinct hallmarks, including acidosis, hypoxia, reactive oxygen species (ROS) generation, and altered ion fluxes, which are crucial targets for early cancer biomarker detection, tumor diagnosis, and therapeutic strategies. Various imaging and sensing techniques have been developed and employed in both research and clinical settings to visualize and monitor cellular and TME dynamics. Among these, ratiometric fluorescence-based sensors have emerged as powerful analytical tools, providing precise and sensitive insights into TME and enabling real-time detection and tracking of dynamic changes. In this comprehensive review, we discuss the latest advancements in ratiometric fluorescent probes designed for the optical mapping of pH, oxygen, ROS, ions, and biomarkers within the TME. We elucidate their structural designs and sensing mechanisms as well as their applications in in vitro and in vivo detection. Furthermore, we explore integrated sensing platforms that reveal the spatiotemporal behavior of complex tumor cultures, highlighting the potential of high-resolution imaging techniques combined with computational methods. This review aims to provide a solid foundation for understanding the current state of the art and the future potential of fluorescent nano- and microparticles in the field of cellular microenvironment sensing.

pH-Switching of the luminescent, redox, and magnetic properties in a spin crossover cobalt(ii) molecular nanomagnet

The ability of mononuclear first-row transition metal complexes as dynamic molecular systems to perform selective functions under the control of an external stimulus that appropriately tunes their properties may greatly impact several domains of molecular nanoscience and nanotechnology. This study focuses on two mononuclear octahedral cobalt(ii) complexes of formula {[CoII(HL)2][CoII(HL)L]}(ClO4)3·9H2O (1) and [CoIIL2]·5H2O (2) [HL = 4'-(4-carboxyphenyl)-2,2':6',2''-terpyridine], isolated as a mixed protonated/hemiprotonated cationic salt or a deprotonated neutral species. This pair of pH isomers constitutes a remarkable example of a dynamic molecular system exhibiting reversible changes in luminescence, redox, and magnetic (spin crossover and spin dynamics) properties as a result of ligand deprotonation, either in solution or solid state. In this last case, the thermal-assisted spin transition coexists with the field-induced magnetisation blockage of "faster" or "slower" relaxing low-spin CoII ions in 1 or 2, respectively. In addition, pH-reversible control of the acid-base equilibrium among dicationic protonated, cationic hemiprotonated, and neutral deprotonated forms in solution enhances luminescence in the UV region. Besides, the reversibility of the one-electron oxidation of the paramagnetic low-spin CoII into the diamagnetic low-spin CoIII ion is partially lost and completely restored by pH decreasing and increasing. The fine-tuning of the optical, redox, and magnetic properties in this novel class of pH-responsive, spin crossover molecular nanomagnets offers fascinating possibilities for advanced multifunctional and multiresponsive magnetic devices for molecular spintronics and quantum computing such as pH-effect spin quantum transformers.

Highly Coupled Seven-Core Fiber for Ratiometric Anti-Phase Sensing

A ratiometric fiber optic temperature sensor based on a highly coupled seven-core fiber (SCF) is proposed and experimentally demonstrated. A theoretical analysis of the SCF's sinusoidal spectral response in transmission configuration is presented. The proposed sensor comprises two SCF devices exhibiting anti-phase transmission spectra. Simple fabrication of the devices is shown by just splicing a segment of a 2 cm long SCF between two single-mode fibers (SMFs). The sensor proved to be robust against light source fluctuations, as a standard deviation of 0.2% was registered in the ratiometric measurements when the light source varied by 12%. Its low-cost detection system (two photodetectors) and the range of temperature detection (25 °C to 400 °C) make it a very attractive and promising device for real industrial applications.

Macropinoscope: Real-Time Simultaneous Tracking of pH and Cathepsin B Activity in Individual Macropinosomes

A fluorescent sensor that allows simultaneous analysis of environmental factors in a limited cellular space is useful for understanding precise molecular interactions in live cells and their biological responses. Macropinocytosis is a ubiquitous endocytic pathway for massive uptake of extracellular fluids, resulting in the formation of macropinosomes. Although macropinocytosis may impact intracellular delivery and cancer proliferation, information on the intracellular behaviors of macropinosomes is limited. Here, we aimed to develop a macropinoscope, a sensor that simultaneously detects pH and cathepsin B activity in individual macropinosomes. A macropinosome-specific marker, dextran (70 kDa), was employed as a platform, onto which fluorescein, Oregon Green, and tetramethylrhodamine were loaded for ratiometric pH sensing and imaging. A cathepsin-B-cleavable peptide sequence bearing sulfo-Cy5 and the quencher BHQ-3 was also mounted; cleavage of the sequence was detected as an increase in sulfo-Cy5 fluorescence. A steep decrease in pH was observed 5-10 min after macropinosome formation, which was accompanied by an immediate increase in cathepsin B activity. Our design concept will lead to the development of other macropinoscopes for the simultaneous detection of other parameters in individual macropinosomes.

Designing Nonconventional Luminescent Materials with Efficient Emission in Dilute Solutions via Modulation of Dynamic Hydrogen Bonds

Nonconventional luminescent materials (NLMs) which do not contain traditional aromatic chromophores are of great interest due to their unique chemical structures, optical properties, and their potential applications in various areas, such as cellular imaging and chemical sensing. However, most reported NLMs show weak or no emission in dilute solutions, which severely limits their applications. In this work, dynamic hydrogen bonds were utilized to design NLMs with efficient emission in dilute solutions. To further validate the results, polymers P1 and P2 were successfully prepared and investigated. It was found that the luminescence quantum efficiency of P1 and P2 at a concentration of 0.1 mg/mL in water solution was 8.9 and 0.6%, respectively. The high efficiency can be attributed to the fact that polymer P1 has more intra- or intermolecular dynamic hydrogen bonds and other short interactions than P2 in dilute solutions, allowing P1 to achieve the through-space conjugation effect to increase the degree of system conjugation, restrict molecular motion, and decrease nonradiative transitions, which can effectively improve luminescence. In addition, polymer P2 exhibits the characteristics of clustering-triggered emission, excitation wavelength-dependent and concentration-dependent fluorescence properties, excellent photobleaching resistance, low cytotoxicity, and selective recognition of Fe³⁺. The present study investigates the manipulation of luminescence properties of NLMs in dilute solutions through the modulation of dynamic hydrogen bonds. This approach can serve as a semi-empirical technique for designing and building innovative NLMs in the times ahead.

Biomimetic Flexible Sensors and Their Applications in Human Health Detection

Bionic flexible sensors are a new type of biosensor with high sensitivity, selectivity, stability, and reliability to achieve detection in complex natural and physiological environments. They provide efficient, energy-saving and convenient applications in medical monitoring and diagnosis, environmental monitoring, and detection and identification. Combining sensor devices with flexible substrates to imitate flexible structures in living organisms, thus enabling the detection of various physiological signals, has become a hot topic of interest. In the field of human health detection, the application of bionic flexible sensors is flourishing and will evolve into patient-centric diagnosis and treatment in the future of healthcare. In this review, we provide an up-to-date overview of bionic flexible devices for human health detection applications and a comprehensive summary of the research progress and potential of flexible sensors. First, we evaluate the working mechanisms of different classes of bionic flexible sensors, describing the selection and fabrication of bionic flexible materials and their excellent electrochemical properties; then, we introduce some interesting applications for monitoring physical, electrophysiological, chemical, and biological signals according to more segmented health fields (e.g., medical diagnosis, rehabilitation assistance, and sports monitoring). We conclude with a summary of the advantages of current results and the challenges and possible future developments.

Perspectives of different colour-emissive nanomaterials in fluorescent ink, LEDs, cell imaging, and sensing of various analytes

In the past 2 decades, multicolour light-emissive nanomaterials have gained significant interest in chemical and biological sciences because of their unique optical properties. These materials have drawn much attention due to their unique characteristics towards various application fields. The development of novel nanomaterials has become the pinpoint for different application areas. In this review, the recent progress in the area of multicolour-emissive nanomaterials is summarized. The different emissions (white, orange, green, red, blue, and multicolour) of nanostructure materials (metal nanoclusters, quantum dots, carbon dots, and rare earth-based nanomaterials) are briefly discussed. The potential applications of different colour-emissive nanomaterials in the development of fluorescent inks, light-emitting diodes, cell imaging, and sensing devices are briefly summarized. Finally, the future perspectives of multicolour-emissive nanomaterials are discussed.

Fluorescence intensity and fluorescence lifetime measurements of various carbon dots as a function of pH

Measurement and monitoring of pH are essential in both the industry and academia. It is therefore important to continue developing novel, low-cost pH sensors that provide increased accuracy over long periods of time. Particularly promising are sensors based on materials that show pH-dependent fluorescence intensity (FI) and lifetime (FL). Carbon dots (CDs) are emerging as promising candidates because of their low cost, ease of manufacturing, low toxicity, and negligible photobleaching. However, little has been done to quantify the FI and FL values of CDs. Here we report the characterisation of the pH-dependent FI and FL of four novel solvothermal synthesised CDs. The fifth CD is used as a reference sample and was synthesised following a published synthesis. The precursors for the CDs include disperse blue 1 dye, phloroglucinol, m-phenylenediamine (m-PD), N, and N-dimethylformamide (DMF). The average diameter size of the CDs ranges from 1.5 to 15 nm. An excitation wavelength of 452 nm with a bandwidth of 45 nm was used to quantify the fluorescence in the pH range 5-9. Three CDs show a decreasing trend in FI with pH, while two CDs show an increasing trend. None of the CDs shows strong FL dependence. The FL changes around 0.5 ± 0.2 ns across the tested pH range. We suggest that the differences in the fluorescence trends can be attributed to the precursors chosen for synthesising the CDs.

Near-infrared-activated anticancer platinum(IV) complexes directly photooxidize biomolecules in an oxygen-independent manner

Conventional light-driven cancer therapeutics require oxygen and visible light to indirectly damage biomolecules, limiting their efficacy in deep, hypoxic tumours. Here we report the use of near-infrared-activated small-molecule Pt(IV) photooxidants to directly oxidize intracellular biomolecules in an oxygen-independent manner, achieving controllable and effective elimination of cancer stem cells. These Pt(IV) complexes accumulate in the endoplasmic reticulum and show low toxicity in the dark. Upon irradiation, the resultant metal-enhanced photooxidation effect causes them to robustly photooxidize survival-related biomolecules, induce intense oxidative stress, disrupt intracellular pH (pHi) homeostasis and initiate nonclassical necrosis. In vivo experiments confirm that the lead photooxidant can effectively inhibit tumour growth, suppress metastasis and activate the immune system. Our study validates the concept of metal-enhanced photooxidation and the subsequent chemotherapeutic applications, supporting the development of such localized photooxidants to directly damage intracellular biomolecules and decrease pHi as a strategy for effective metal-based drugs.

A water-soluble fluorescent pH probe and its application for monitoring lysosomal pH changes in living cells

Intracellular pH plays a crucial role in many cellular processes, and abnormal intracellular pH has been linked to common diseases such as cancer and Alzheimer's. To address this issue, a water-soluble fluorescent pH probe was designed based on the protonation/deprotonation of the 4-methylpiperazin-1-yl group, using dicyanoisophorone as the fluorophore. In the neutral form of the probe, fluorescence is quenched due to charge transfer from the 4-methylpiperazin-1-yl group to the fluorophore upon excitation. Under acidic conditions, protonation of the 4-methylpiperazin-1-yl group inhibits the photoinduced electron transfer process, leading to an increase in fluorescence intensity. Density-functional theory calculations also verified the fluorescence OFF-ON mechanism. The probe exhibits high selectivity, photostability, fast response to pH changes, and low cytotoxicity to cells. Additionally, the probe selectively accumulates in lysosomes, with a high Pearson coefficient (0.95) using LysoTracker Green DND-26 as a reference. Notably, the probe can monitor lysosomal pH changes in living cells and track pH changes stimulated by chloroquine. We anticipate that the probe has potential for diagnosing pH-related diseases.

Supramolecular Dimer as High-Performance pH Probe: Study on the Fluorescence Properties of Halogenated Ligands in Rigid Schiff Base Complex

The development of high-performance fluorescence probes has been an active area of research. In the present work, two new pH sensors Zn-3,5-Cl-saldmpn and Zn-3,5-Br-saldmpn based on a halogenated Schiff ligand (3,5-Cl-saldmpn = N, N'-(3,3'-dipropyhnethylamine) bis (3,5-chlorosalicylidene)) with linearity and a high signal-to-noise ratio were developed. Analyses revealed an exponential intensification in their fluorescence emission and a discernible chromatic shift upon pH increase from 5.0 to 7.0. The sensors could retain over 95% of their initial signal amplitude after 20 operational cycles, demonstrating excellent stability and reversibility. To elucidate their unique fluorescence response, a non-halogenated analog was introduced for comparison. The structural and optical characterization suggested that the introduction of halogen atoms can create additional interaction pathways between adjacent molecules and enhance the strength of the interaction, which not only improves the signal-to-noise ratio but also forms a long-range interaction process in the formation of the aggregation state, thus enhancing the response range. Meanwhile, the above proposed mechanism was also verified by theoretical calculations.

Spiropyran-based chromic hydrogels for CO2 absorption and detection

By enabling rapid, cost-effective, user-friendly and in situ detection of carbon dioxide, colorimetric CO₂ sensors are of relevance for a variety of fields. However, it still remains a challenge the development of optical chemosensors for CO₂ that combine high sensitivity, selectivity and reusability with facile integration into solid materials. Herein we pursued this goal by preparing hydrogels functionalized with spiropyrans, a well-known class of molecular switches that undergo different color changes upon application of light and acid stimuli. By varying the nature of the substituents of the spiropyran core, different acidochromic responses are obtained in aqueous media that allow discriminating CO₂ from other acid gases (e.g., HCl). Interestingly, this behavior can be transferred to functional solid materials by synthesizing polymerizable spiropyran derivatives, which are used to prepare hydrogels. These materials preserve the acidochromic properties of the incorporated spiropyrans, thus leading to selective, reversible and quantifiable color changes upon exposure to different CO₂ amounts. In addition, CO₂ desorption and, therefore, recovery of the initial state of the chemosensor is favored by irradiation with visible light. This makes spiropyran-based chromic hydrogels promising systems for the colorimetric monitorization of carbon dioxide in a diversity of applications.

Sensors-integrated organ-on-a-chip for biomedical applications

As a promising new micro-physiological system, organ-on-a-chip has been widely utilized for in vitro pharmaceutical study and tissues engineering based on the three-dimensional constructions of tissues/organs and delicate replication of in vivo-like microenvironment. To better observe the biological processes, a variety of sensors have been integrated to realize in-situ, real-time, and sensitive monitoring of critical signals for organs development and disease modeling. Herein, we discuss the recent research advances made with respect to sensors-integrated organ-on-a-chip in this overall review. Firstly, we briefly explore the underlying fabrication procedures of sensors within microfluidic platforms and several classifications of sensory principles. Then, emphasis is put on the highlighted applications of different types of organ-on-a-chip incorporated with various sensors. Last but not least, perspective on the remaining challenges and future development of sensors-integrated organ-on-a-chip are presented.

Highly pH-Responsive Sensor Based on a EuIII Metal-Organic Framework with Efficient Recognition of Arginine and Lysine in Living Cells

A lanthanide-based three-dimensional metal-organic framework with excellent water, acid/base, and solvent stability, namely {[(CH3)2NH2]0.7[Eu2(BTDBA)1.5(lac)0.7(H2O)2]·2H2O·2DMF·2CH3CN}n (JXUST-29, H4BTDBA = 4',4‴-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), Hlac = lactic acid), has been synthesized and characterized. Since the N atoms of the thiadiazole group will not coordinate with lanthanide ions, JXUST-29 has a free basic N-site accessible to small H+ ions, which allows it to be used as a promising pH fluorescence sensor. Interestingly, the luminescence signal was significantly enhanced, with an approximately 54-fold enhancement in the emission intensity when the pH value was increased from 2 to 5, which is the typical behavior of pH probes. In addition, JXUST-29 can also be used as a luminescence sensor to detect l-arginine (Arg) and l-lysine (Lys) in an aqueous solution through fluorescence enhancement and the blue-shift effect. The detection limits were 0.023 and 0.077 μM, respectively. In addition, JXUST-29-based devices were designed and developed to facilitate detection. Importantly, JXUST-29 is also capable of detecting and sensing Arg and Lys in living cells.

Dual-Responsive and Reusable Optical Sensors Based on 2,3-Diaminoquinoxalines for Acidity Measurements in Low-pH Aqueous Solutions

This work is focused on the age-old challenge of developing optical sensors for acidity measurements in low-pH aqueous solutions (pH < 5). We prepared halochromic (3-aminopropyl)amino-substituted quinoxalines QC1 and QC8 possessing different hydrophilic-lipophilic balance (HLB) and investigated them as molecular components of pH sensors. Embedding the hydrophilic quinoxaline QC1 into the agarose matrix by sol-gel process allows for fabrication of pH responsive polymers and paper test strips. The emissive films thus obtained can be used for a semi-quantitative dual-color visualization of pH in aqueous solution. Being exposed to acidic solutions with pH in the range of 1-5, they rapidly give different color changes when the analysis is performed in daylight or under irradiation at 365 nm. Compared with classical non-emissive pH indicators, these dual-responsive pH sensors allow for an increase in the accuracy of pH measurements, particularly in complex environmental samples. pH indicators for quantitative analysis can be prepared by the immobilization of amphiphilic quinoxaline QC8 using Langmuir-Blodgett (LB) and Langmuir-Schäfer (LS) techniques. Compound QC8 possessing two long alkyl chains (n-C₈H₁₇) forms stable Langmuir monolayers at the air-water interface, and these monolayers can be successfully transferred onto hydrophilic quartz and hydrophobic polyvinylchlorid (PVC) substrates using LB and LS techniques, respectively. The 30-layer films thus obtained are emissive, reveal excellent stability, and can be used as dual-responsive pH indicators for quantitative measurements in real-world samples with pH in the range of 1-3. The films can be regenerated by immersing them in basic aqueous solution (pH = 11) and can be reused at least five times.

Enhancing Methotrexate Delivery in the Brain by Mesoporous Silica Nanoparticles Functionalized with Cell-Penetrating Peptide using in Vivo and ex Vivo Monitoring

The blood-brain barrier (BBB) acts as a physical/biochemical barrier that protects brain parenchyma from potential hazards exerted by different xenobiotics found in the systemic circulation. This barrier is created by "a lipophilic gate" as well as a series of highly organized influx/efflux mechanisms. The BBB bottleneck adversely affects the efficacy of chemotherapeutic agents in treating different CNS malignancies such as glioblastoma, an aggressive type of cancer affecting the brain. In the present study, mesoporous silica nanoparticles (MSNs) were conjugated with the transactivator of transcription (TAT) peptide, a cell-penetrating peptide, to produce MSN-NH-TAT with the aim of improving methotrexate (MTX) penetration into the brain. The TAT-modified nanosystem was characterized by Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and N₂ adsorption-desorption analysis. In vitro hemolysis and cell viability studies confirmed the biocompatibility of the MSN-based nanocarriers. In addition, in vivo studies showed that the MTX-loaded MSN-NH-TAT improved brain-to-plasma concentration ratio, brain uptake clearance, and the drug's blood terminal half-life, compared with the use of free MTX. Taken together, the results of the present study indicate that MSN functionalization with TAT is crucial for delivery of MTX into the brain. The present nanosystem represents a promising alternative drug carrier to deliver MTX into the brain via overcoming the BBB.

Red-shifted and pH-responsive imidazole-based azo dyes with potent antimicrobial activity

A novel route is described to obtain 2-aminoimidazole azo dyes with a unique substituent pattern in the heteroaryl unit that provides halochromic properties, exhibiting vibrant colours that change from magenta to deep blue. Potent antimicrobial properties against infectious yeasts were demonstrated. No cytotoxicity was detected for concentrations lower than 16 μg mL^-1.

Fluorescent Probes as a Tool in Diagnostic and Drug Delivery Systems

Over the last few years, the development of fluorescent probes has received considerable attention. Fluorescence signaling allows noninvasive and harmless real-time imaging with great spectral resolution in living objects, which is extremely useful for modern biomedical applications. This review presents the basic photophysical principles and strategies for the rational design of fluorescent probes as visualization agents in medical diagnosis and drug delivery systems. Common photophysical phenomena, such as Intramolecular Charge Transfer (ICT), Twisted Intramolecular Charge Transfer (TICT), Photoinduced Electron Transfer (PET), Excited-State Intramolecular Proton Transfer (ESIPT), Fluorescent Resonance Energy Transfer (FRET), and Aggregation-Induced Emission (AIE), are described as platforms for fluorescence sensing and imaging in vivo and in vitro. The presented examples are focused on the visualization of pH, biologically important cations and anions, reactive oxygen species (ROS), viscosity, biomolecules, and enzymes that find application for diagnostic purposes. The general strategies regarding fluorescence probes as molecular logic devices and fluorescence–drug conjugates for theranostic and drug delivery systems are discussed. This work could be of help for researchers working in the field of fluorescence sensing compounds, molecular logic gates, and drug delivery.

Development of a palm-sized bioelectronic sensing device for protein detection in milk samples

The present study relates a portable optical sensing device supported by a small single-board (SBC) computer. The electronic architectural avenue connects the SBC with a camera, LED lights and a monitor. A 'sensor integration unit' has been linked with the device where the biological reactions were performed and assessed based on the concentration-dependent optical signal outputs. This setup can detect the generation of colors and distinguish their changes in the RGB intensity scale with an accuracy of a single pixel unit. A predefined range of values was obtained and fed to the device that can quantitatively sense the molecule of interest on the sensing matrix. The device has a touchscreen interactive panel that allows users to manually set experimental conditions and connect the entire measurement process to the cloud storage for backup information. We have considered detecting Alkaline Phosphatase (ALP) quantitatively from standard solutions as well as in milk samples as a proof-of-concept protein molecule. The device has shown exceptional analytical performance for lower and higher concentration ranges (0-100 U/mL and 100-1000 U/mL) with correlation coefficient values of 0.99. The detection limit of ALP was determined to be 0.1 U/mL, and the average time of a sample assessment was recorded to be 15 s. The device has also been tested against ALP-spiked milk samples to check its effectiveness and commercial viability. The outcome of the real-time assessment was sensitive and efficient, indicating its direct commercial and clinical importance towards colorimetric detection for diverse macromolecules.

Cellulose-Based Fluorescent Material for Extreme pH Sensing and Smart Printing Applications

Environment-responsive fluorescence materials are being widely investigated for instrument-free determination of various environmental factors. However, developing an eco-friendly cellulose-based fluorescent pH sensor for sensing extreme acidity and alkalinity is still challenging. Herein, a highly fluorescent and multifunctional material is developed from biopolymer-based cellulose acetate. A biopolymer-based structure containing responsive functional groups such as -C═O and -NH is constructed by chemically bonding 5-amino-2,3-dihydrophthalazine-1,4-dione (luminol) onto cellulose acetate using 4,4'-diphenylmethane diisocyanate (MDI) as a cross-linking agent. The prepared material (Lum-MDI-CA) is characterized by UV-vis, Fourier transform infrared, ¹H NMR, ¹³C NMR spectroscopies, and fluorescence techniques. The material exhibits excellent aqua blue fluorescence and demonstrates extreme pH sensing applications. Interesting results are further revealed after adding a pH-unresponsive dye such as MTPP as the reference to develop the ratiometric method. The ratiometric system clearly differentiates the extreme acidic pH 1 from pH 2 and extreme alkaline pH 12, 13, and 14 by visual and fluorescence color change response under a narrow pH range. In addition, the material is fabricated into transparent flexible fluorescent films which demonstrate an outstanding UV shielding, security printing, and haze properties for smart food packaging and printing applications.