Photoacoustic Chemical Imaging Sodium Nano-Sensor Utilizing a Solvatochromic Dye Transducer for In Vivo Application

Sodium has many vital and diverse roles in the human body, including maintaining the cellular pH, generating action potential, and regulating osmotic pressure. In cancer, sodium dysregulation has been correlated with tumor growth, metastasis, and immune cell inhibition. However, most in vivo sodium measurements are performed via Na23 NMR, which is handicapped by slow acquisition times, a low spatial resolution (in mm), and low signal-to-noise ratios. We present here a plasticizer-free, ionophore-based sodium-sensing nanoparticle that utilizes a solvatochromic dye transducer to circumvent the pH cross-sensitivity of most previously reported sodium nano-sensors. We demonstrate that this nano-sensor is non-toxic, boasts a 200 μM detection limit, and is over 1000 times more selective for sodium than potassium. Further, the in vitro photoacoustic calibration curve presented demonstrates the potential of this nano-sensor for performing the in vivo chemical imaging of sodium over the entire physiologically relevant concentration range.

MID-FTIR-PLS Chemometric Analysis of Cr(VI) from Aqueous Solutions Using a Polymer Inclusion Membrane-Based Sensor

A partial least squares (PLS) quantitative chemometric method based on the analysis of the mid-Fourier transform infrared spectroscopy (MID-FTIR) spectrum of polymer inclusion membranes (PIMs) used for the extraction of Cr(VI) from aqueous media is developed. The system previously optimized considering the variables membrane composition, extraction time, and pH, is characterized in terms of its adsorption isotherm, distribution coefficient, extraction percent, and enrichment factor. A Langmuir-type adsorption behavior with KL = 2199 cm3/mmol, qmax = 0.188 mmol/g, and 0 < RL < 1 indicates that metal adsorption is favorable. The characterization of the extraction reaction is performed as well, showing a 1:1 Cr(VI):Aliquat 336 ratio, in agreement with solvent extraction data. The principal component analysis (PCA) of the PIMs reveals a complex pattern, which is satisfactorily simplified and related to Cr(VI) concentrations through the use of a variable selection method (iPLS) in which the bands in the ranges 3451-3500 cm-1 and 3751-3800 cm-1 are chosen. The final PLS model, including the 100 wavelengths selected by iPLS and 10 latent variables, shows excellent parameter values with root mean square error of calibration (RMSEC) of 3.73115, root mean square error of cross-validation (RMSECV) of 6.82685, bias of -1.91847 × 10-13, cross-validation (CV) bias of 0.185947, R2 Cal of 0.98145, R2 CV of 0.940902, recovery% of 104.02 ± 4.12 (α = 0.05), sensitivity% of 0.001547 ppb, analytical sensitivity (γ) of 3.8 ppb, γ-1: 0.6 ppb-1, selectivity of 0.0155, linear range of 5.8-100 ppb, limit of detection (LD) of 1.9 ppb, and limit of quantitation (LQ) of 5.8 ppb. The developed PIM sensor is easy to implement as it requires few manipulations and a reduced number of chemical compounds in comparison to other similar reported systems.

Imaging of CO2 and Dissolved Inorganic Carbon via Electrochemical Acidification-Optode Tandem

Dissolved inorganic carbon (DIC) is a key component of the global carbon cycle and plays a critical role in ocean acidification and proliferation of phototrophs. Its quantification at a high spatial resolution is essential for understanding various biogeochemical processes. We present an analytical method for 2D chemical imaging of DIC by combining a conventional CO2 optode with localized electrochemical acidification from a polyaniline (PANI)-coated stainless-steel mesh electrode. Initially, the optode response is governed by local concentrations of free CO2 in the sample, corresponding to the established carbonate equilibrium at the (unmodified) sample pH. Upon applying a mild potential-based polarization to the PANI mesh, protons are released into the sample, shifting the carbonate equilibrium toward CO2 conversion (>99%), which corresponds to the sample DIC. It is herein demonstrated that the CO2 optode-PANI tandem enables the mapping of free CO2 (before PANI activation) and DIC (after PANI activation) in complex samples, providing high 2D spatial resolution (approx. 400 μm). The significance of this method was proven by inspecting the carbonate chemistry of complex environmental systems, including the freshwater plant Vallisneria spiralis and lime-amended waterlogged soil. This work is expected to pave the way for new analytical strategies that combine chemical imaging with electrochemical actuators, aiming to enhance classical sensing approaches via in situ (and reagentless) sample treatment. Such tools may provide a better understanding of environmentally relevant pH-dependent analytes related to the carbon, nitrogen, and sulfur cycles.

Optical Oxygen Sensors Show Reversible Cross-Talk and/or Degradation in the Presence of Nitrogen Dioxide

A variety of luminescent dyes including the most common indicators for optical oxygen sensors were investigated in regard to their stability and photophysical properties in the presence of nitrogen dioxide. The dyes were immobilized in polystyrene and subjected to NO₂ concentrations from 40 to 5500 ppm. The majority of dyes show fast degradation of optical properties due to the reaction with NO₂. The class of phosphorescent metalloporphyrins shows the highest resistance against nitrogen dioxide. Among them, palladium(II) and platinum(II) complexes of octasubstituted sulfonylated benzoporphyrins are identified as the most stable dyes with almost no decomposition in the presence of NO₂. The phosphorescence of these dyes is reversibly quenched by nitrogen dioxide. Immobilized in various polymeric matrices, the sulfonylated Pt(II) benzoporphyrin demonstrates about one order of magnitude more efficient quenching by NO₂ than by molecular oxygen. Our study demonstrates that virtually all commercially available and reported optical oxygen sensors are likely to show either irreversible decomposition in the presence of nitrogen dioxide or reversible luminescence quenching. They should be used with extreme caution if NO₂ is present in relatively high concentrations or it may be generated from other species such as nitric oxide. As an important consequence of nearly anoxic systems, production of nitrogen dioxide or nitric oxide may be therefore erroneously interpreted as an increase in oxygen concentration.

Integration of Response Surface Methodology (RSM) and Principal Component Analysis (PCA) as an Optimization Tool for Polymer Inclusion Membrane Based-Optodes Designed for Hg(II), Cd(II), and Pb(II)

An optimization of the composition of polymer inclusion membrane (PIM)-based optodes, and their exposure times to metal ion solutions (Hg(II), Cd(II), and Pb(II)) was performed using two different chromophores, diphenylthiocarbazone (dithizone) and 1-(2-pyridylazo)-2-naphthol (PAN). Four factors were evaluated (chromophore (0.06-1 mg), cellulose triacetate (25-100 mg) and plasticizer amounts (25-100 mg), and exposure time (20-80 min)). Derringer's desirability functions values were employed as response variables to perform the optimization obtained from the results of three different processes of spectral data treatment: two full-spectrum methods (M1 and M3) and one band-based method (M2). The three different methods were compared using a heatmap of the coefficients and dendrograms of the Principal Component Analysis (PCA)reductions of their desirability functions. The final recommended M3 processing method, i.e., using the scores values of the first two principal components in PCA after subtraction of the normalized spectra of the membranes before and after complexation, gave more discernable differences between the PIMs in the Design of Experiments (DoE), as the nodes among samples appeared at longer distances and varyingly distributed in the dendrogram analysis. The optimal values were time of 35-65 min, 0.53 mg-1.0 mg of chromophores, plasticizers 34.4-71.9 of chromophores, and 62.5-100 mg of CTA, depending on the metal ion. In addition, the method yielded the best outcomes in terms of interpretability and an easily discernable color change so that it is recommended as a novel optimization method for this kind of PIM optode.

Bacterial Respiration Used as a Proxy to Evaluate the Bacterial Load in Cooling Towers

Evaporative cooling towers to dissipate excess process heat are essential installations in a variety of industries. The constantly moist environment enables substantial microbial growth, causing both operative challenges (e.g., biocorrosion) as well as health risks due to the potential aerosolization of pathogens. Currently, bacterial levels are monitored using rather slow and infrequent sampling and cultivation approaches. In this study, we describe the use of metabolic activity, namely oxygen respiration, as an alternative measure of bacterial load within cooling tower waters. This method is based on optical oxygen sensors that enable an accurate measurement of oxygen consumption within a closed volume. We show that oxygen consumption correlates with currently used cultivation-based methods (R² = 0.9648). The limit of detection (LOD) for respiration-based bacterial quantification was found to be equal to 1.16 × 10⁴ colony forming units (CFU)/mL. Contrary to the cultivation method, this approach enables faster assessment of the bacterial load with a measurement time of just 30 min compared to 48 h needed for cultivation-based measurements. Furthermore, this approach has the potential to be integrated and automated. Therefore, this method could contribute to more robust and reliable monitoring of bacterial contamination within cooling towers and subsequently increase operational stability and reduce health risks.

Determination of Polyhexamethylene Biguanide Hydrochloride Using a Lactone-Rhodamine B-Based Fluorescence Optode

A new determination method for polyhexamethylene biguanide hydrochloride (PHMB) using a lactone-rhodamine B (L-RB) based fluorescence optode has been developed. The optode membrane consists of 2-nitrophenyl octyl ether as a plasticizer, L-RB, and poly (vinyl chloride). The optode responds to tetrakis (4-fluorophenyl) borate, sodium salt (NaTPBF) in the μM range. The fluorescence intensity of the L-RB film for PHMB solution containing 20 μM NaTPBF decreased linearly as the concentration of the PHMB solution increased in the concentration range from 0 to 8.0 μM, which shows that PHMB with a concentration range of 0 to 8.0 μM is determined by the L-RB film optode. The concentration of PHMB in the contact lens detergents by the proposed method was in accord with its nominal concentration.

Ionophore-Based Optical Sensor for Urine Creatinine Determination

Creatinine is a metabolite present in urine, and its concentration is used to diagnose and monitor kidney performance. For that reason, the development of new sensors to analyze this metabolite and obtain accurate results in a short period of time is necessary. An optical disposable sensor for monitoring creatinine levels in urine is described. The system, based on a new aryl-substituted calix[4]pyrrole synthetic receptor, has an unusual coextraction scheme. Due to the low p K_a values of creatininium (p K_a 4.8), a careful selection of a lipophilic pH indicator that works in acid medium is required. The sensor components were optimized, and the new sensor displays a good response time to creatinine (approximately 3 min) over a wide dynamic range (from 1 × 10^-5 to 1 × 10^-2 M). Moreover, the optical selectivity coefficients obtained for creatinine over common cations present in urine meet the requirements for real sample measurements. With a good sensor-to-sensor reproducibility (RSD, 5.1-6.9% in the middle of the range), this method provides a simple, quick, cost-effective, and selective alternative to the conventional methodology based on Jaffé's reaction.

Imaging Sodium Flux during Action Potentials in Neurons with Fluorescent Nanosensors and Transparent Microelectrodes

Sodium flux plays a pivotal role in neurobiological processes including initiation of action potentials and regulation of neuronal cell excitability. However, unlike the wide range of fluorescent calcium indicators used extensively for cellular studies, the choice of sodium probes remains limited. We have previously demonstrated optode-based nanosensors (OBNs) for detecting sodium ions with advantageous modular properties such as tunable physiological sensing range, full reversibility, and superb selectivity against key physiological interfering ion potassium. (1) Motivated by bridging the gap between the great interest in sodium imaging of neuronal cell activity as an alternative to patch clamp and limited choices of optical sodium indicators, in this Letter we report the application of nanosensors capable of detecting intracellular sodium flux in isolated rat dorsal root ganglion neurons during electrical stimulation using transparent microelectrodes. Taking advantage of the ratiometric detection scheme offered by this fluorescent modular sensing platform, we performed dual color imaging of the sensor to monitor the intracellular sodium currents underlying trains of action potentials in real time. The combination of nanosensors and microelectrodes for monitoring neuronal sodium dynamics is a novel tool for investigating the regulatory role of sodium ions involved during neural activities.

Ion-Switchable Quantum Dot Förster Resonance Energy Transfer Rates in Ratiometric Potassium Sensors

The tools for optically imaging cellular potassium concentrations in real-time are currently limited to a small set of molecular indicator dyes. Quantum dot-based nanosensors are more photostable and tunable than organic indicators, but previous designs have fallen short in size, sensitivity, and selectivity. Here, we introduce a small, sensitive, and selective nanosensor for potassium measurements. A dynamic quencher modulates the fluorescence emitted by two different quantum dot species to produce a ratiometric signal. We characterized the potassium-modulated sensor properties and investigated the photonic interactions within the sensors. The quencher's protonation changes in response to potassium, which modulates its Förster radiative energy transfer rate and the corresponding interaction radii with each quantum dot species. The nanosensors respond to changes in potassium concentrations typical of the cellular environment and thus provide a promising tool for imaging potassium fluxes during biological events.

Gel encapsulation of glucose nanosensors for prolonged in vivo lifetime

BACKGROUND

Fluorescent glucose-sensitive nanosensors have previously been used in vivo to track glucose concentration changes in interstitial fluid. However, this technology was limited because of loss of fluorescence intensity due to particle diffusion from the injection site. In this study, we encapsulated the nanosensors into injectable gels to mitigate nanosensor migration in vivo.

METHODS

Glucose-sensitive nanosensors were encapsulated in two different commercially available gelling agents: gel 1 and gel 2. Multiple formulations of each gel were assessed in vitro for their nanosensor encapsulation efficiency, permeability to glucose, and nanosensor retention over time. The optimal formulation for each gel, as determined from the in vitro assessment, was then tested in mice, and the lifetime of the encapsulated nanosensors was compared with controls of nanosensors without gel.

RESULTS

Five gel formulations had encapsulation efficiencies of the nanosensors greater than 90%. Additionally, they retained up to 20% and 40% of the nanosensors over 24 h for gel 1 and gel 2, respectively. In vivo, both gels prevented diffusion of glucose nanosensors at least three times greater than the controls.

CONCLUSIONS

Encapsulating glucose nanosensors in two injectable gels prolonged nanosensor lifetime in vivo; however, the lifetime must still be increased further to be applicable for diabetes monitoring.

In vivo histamine optical nanosensors

In this communication we discuss the development of ionophore based nanosensors for the detection and monitoring of histamine levels in vivo. This approach is based on the use of an amine-reactive, broad spectrum ionophore which is capable of recognizing and binding to histamine. We pair this ionophore with our already established nanosensor platform, and demonstrate in vitro and in vivo monitoring of histamine levels. This approach enables capturing rapid kinetics of histamine after injection, which are more difficult to measure with standard approaches such as blood sampling, especially on small research models. The coupling together of in vivo nanosensors with ionophores such as nonactin provide a way to generate nanosensors for novel targets without the difficult process of designing and synthesizing novel ionophores.

IMAGING OF OXYGEN DYNAMICS WITHIN THE ENDOLITHIC ALGAL COMMUNITY OF THE MASSIVE CORAL PORITES LOBATA(1)

We used transparent planar oxygen optodes and a luminescence lifetime imaging system to map (at a pixel resolution of <200 μm) the two-dimensional distribution of O2 within the skeleton of a Porites lobata colony. The O2 distribution was closely correlated to the distribution of the predominant endolithic microalga, Ostreobium quekettii Bornet et Flahault that formed a distinct green band inside the skeleton. Oxygen production followed the outline of the Ostreobium band, and photosynthetic O2 production was detected at only 0.2 μmol photons m(-2)  · s(-1) , while saturation occurred at ∼37 μmol photons m(-2)  · s(-1) . Oxygen levels varied from ∼60% to 0% air saturation in the illuminated section of the coral skeleton in comparison to the darkened section. The O2 production within the Ostreobium band was lower in the region below the upward facing surface of the coral and elevated on the sides. Oxygen consumption in darkness was also greatest within the Ostreobium zone, as well as in the white skeleton zone immediately below the corallites. The rate of O2 depletion was not constant within zones and between zones, showing pronounced heterogeneity in endolithic respiration. When the coral was placed in darkness after a period of illumination, O2 levels declined by 50% within 20 min and approached steady-state after 40-50 min in darkness. Our study demonstrates the use of an important new tool in endolith photobiology and presents the first data of spatially resolved O2 concentration and its correlation to the physical structures and specific zones responsible for O2 production and consumption within the coral skeleton.