Chemiluminescent Ion Sensing Platform Based on Ionophores

A portable paper-based sensor for simultaneous determination of sodium and potassium ions in the human plasma matrix

Accurate determination of sodium and potassium ions in biological fluids is crucial for managing various health conditions, as these electrolytes play a vital role in regulating physiological processes and maintaining overall well-being. A low-cost portable paper-based sensor has been developed for the simultaneous determination of sodium and potassium in the human plasma matrix. It comprises three electrodes on a single paper substrate: a solid-state polyvinyl butyral reference electrode, a sodium selective electrode and a potassium selective electrode. The sensor utilizes conductive functionalized multi-walled carbon nanotubes, selective ionophores and dyes to enhance sensing capabilities. It demonstrates high selectivity for sodium and potassium ions, with a linear range of 10-6 to 10-2 M and a Nernstian response (slopes of 59.08 ± 0.32 and 59.15 ± 0.28 mV per decade for sodium and potassium, respectively). The sensor provides a reproducible stable potential over 180 days and a dynamic response time of 10 s. The described paper-based sensor is an excellent tool for point-of-care analysis of sodium and potassium imbalances due to its simplicity, cost-effectiveness and disposability. It provides fast and reliable determination of sodium and potassium ions in the human plasma matrix, making it a valuable tool for managing their imbalances in clinical settings.

Multi-level structured nanoparticles prepared by microfluidics control method for efficient and sensitive chemiluminescence immunoassay

The properties of nanomaterials are heavily influenced by their size effects. Utilizing the self-assembly principle offers a promising avenue for crafting innovative nanomaterials, yet controlling this process at the microscopic level presents significant challenges, hindering effective regulation of nanomaterial morphology. Microfluidic technology, however, offers precise control over fluid velocities within microchannels, enabling micro-level manipulation. In this study, we synthesized amphiphilic molecules HP (Hematin@NH2-PEG-COOH) through hematin modification, leveraging microfluidic techniques to encapsulate luminol within HP molecules, resulting in the formation of highly efficient chemiluminescence (CL) HPL (HP@Luminol) nanoparticles. The size effects and intricate multi-level structures achieved during encapsulation endowed these nanoparticles with enhanced catalytic capabilities for CL. Finally, we used HPL nanoparticles as luminescent markers to develop a CL immunosensor for the sensitive detection of the tumor marker carcinoembryonic antigen (CEA), achieving satisfactory results. This innovative approach not only expands the repertoire of nanomaterial design and synthesis but also offers a practical solution for sensitive biomarker detection. Overall, this research introduces a novel strategy for designing and fabricating advanced nanomaterials, underscoring the potential of microfluidic technology in nanoscience and biosensing applications.

Ionophore-Based SERS Sensing for Electrolyte Cations

We present here a surface-enhanced Raman spectroscopy (SERS)-based platform for selectively detecting electrolyte cations. This platform facilitates the reorientation of the chromoionophore I (CHI) molecule positioned on the surface of silver nanoparticles, regulated by the targeted electrolyte cation within the ionophore-based ion-selective sensing framework. When exposed to the target ions, leading to deprotonation, the aromatic plane of the CHI molecule shifts from an endwise to an edgewise configuration on the SERS substrate surface. This reorientation improves the coupling of the induced dipole within the molecule and the induced electromagnetic field normal to the surface, leading to a heightened and more discernible SERS signal. Additionally, NMR data revealed a protonation-dependent conformational change in the CHI molecules. Upon protonation, the side chain of the CHI molecule extends away from its aromatic ring, whereas upon deprotonation, the carbon chain folds back and closely approaches the edge of the aromatic plane, further confirming this conclusion. Using Ca2+ and Na+ as examples, this method shows a detection limit of 0.1 μM for Ca2+ and 1 μM for Na+ with high selectivity. The successful application of the versatile and rapidly advancing SERS technique for electrolyte cation detection shows a promising pathway for enhancing current ion detection capabilities. As a preliminary demonstration, the total Ca2+ concentration in undiluted human serum was successfully determined, with common matrix interference effectively circumvented.

Maintenance-free antifouling polymeric membrane potentiometric sensors based on self-polishing coatings

Polymeric membrane ion-selective electrodes (ISEs) have been widely used in environmental monitoring. However, in complicated marine environments, marine biofouling usually becomes a sticky problem for these electrodes. Herein, for the first time, a novel maintenance-free antifouling potentiometric marine sensor based on a self-polishing coating (SPC) is proposed. The SPC is synthesized by using the seeded emulsion polymerization method based on the triisopropylsilyl methacrylate monomer as the regulator of the self-renewal rate. This coating can be simply modified onto the electrode surface by drop-casting. The silyl acrylate side groups of the obtained SPC on the sensor surface can be hydrolyzed in the marine alkaline medium. The shear movement of seawater driven by sea waves, wind, gravity, or vibration removes the leftover (fouled) brittle polymer backbone and thus the fouling marine microorganisms. As a proof-of-concept experiment, a polymeric membrane Ca2+-ISE is chosen as a model. Compared to the unmodified electrode, the SPC-coated Ca2+-ISE exhibits remarkable improved antifouling properties in terms of superior anti-adhesive abilities towards marine microorganisms, such as bacterial cells and algae and excellent long-term stability even in the presence of high levels of marine microorganisms. Since no additional manual maintenance is required for maintaining the antifouling abilities of the sensor, the proposed self-polishing sensor may lay an important foundation for construction of unattended long-term potentiometric monitoring systems in real marine environments.

Direct and Specific Detection of Glyphosate Using a Phosphatase-like Nanozyme-Mediated Chemiluminescence Strategy

Most organophosphorus pesticide (OP) sensors reported in the literature rely on the inhibition effect of OPs on the activity of acetylcholinesterase (AChE), which suffer from the drawbacks of lack of selective recognition of OPs, high cost, and poor stability. Herein, we proposed a novel chemiluminescence (CL) strategy for the direct detection of glyphosate (an organophosphorus herbicide) with high sensitivity and specificity, which is based on the porous hydroxy zirconium oxide nanozyme (ZrO_X-OH) obtained via a facile alkali solution treatment of UIO-66. ZrO_X-OH displayed excellent phosphatase-like activity, which could catalyze the dephosphorylation of 3-(2'-spiroadamantyl)-4-methoxy-4-(3'-phosphoryloxyphenyl)-1,2-dioxetane (AMPPD) to generate strong CL. The experimental results showed that the phosphatase-like activity of ZrO_X-OH is closely related to the content of hydroxyl groups on their surface. Interestingly, ZrO_X-OH with phosphatase-like properties exhibited a unique response to glyphosate because of the consumption of the surface hydroxyl group by the unique carboxyl group of glyphosates and was thus employed to develop a CL sensor for direct and selective detection of glyphosate without using bio-enzymes. The recovery for glyphosate detection of cabbage juice ranged from 96.8 to 103.0%. We believe that the as-proposed CL sensor based on ZrO_X-OH with phosphatase-like properties supplies a simpler and more highly selective approach for OP assay and provides a new method for the development of CL sensors for the direct analysis of OPs in real samples.

Surface PEGylation of ionophore-based microspheres enables determination of serum sodium and potassium ion concentration under flow cytometry

We present here an ionophore-based ion-selective optode (ISO) platform to detect potassium and sodium concentrations in serum through flow cytometry. The ion-selective microsensors were based on polyethylene glycol (PEG)-modified polystyrene (PS) microspheres (PEG-PS). Ratiometric response curves were observed using peak channel fluorescence intensities for K⁺ (10^-6 M to 0.1 M) and Na⁺ (10^-4 M to 0.2 M) with sufficient selectivity for clinical diagnosis. Due to the matrix effect, proteins such as albumin and immunoglobulin caused an obvious increase in response for serum sample determination. To solve this problem, 4-arm PEG chains were covalently attached onto the surface of PS microspheres through a two-step reaction, which improved the stability and combated pollution of microspheres. As a preliminary application, potassium and sodium concentrations in human serums were successfully determined by the PEG-PS microsensors through flow cytometry.

Perspective on fluorescence cell imaging with ionophore-based ion-selective nano-optodes

Inorganic ions are ubiquitous in all kinds of cells with highly dynamic spatial and temporal distribution. Taking advantage of different types of fluorescent probes, fluorescence microscopic imaging and quantitative analysis of ion concentrations in cells have rapidly advanced. A family of fluorescent nanoprobes based on ionophores has emerged in recent years with the potential to establish a unique platform for the analysis of common biological ions including Na+, K+, Ca2+, Cl-, and so on. This article aims at providing a retrospect and outlook of ionophore-based ion-selective nanoprobes and the applications in cell imaging.

Recent advances and perspectives of enzyme-based optical biosensing for organophosphorus pesticides detection

The overuse or abuse of organophosphorus pesticides (OPs) can bring about severe contamination problems in foodstuff and the environment, which will seriously threaten human health and the ecosystem's cycle. Hence, it is in high demand to establish sensitive, portable, specific, and cost-effective methods for monitoring OPs to control food safety, protect the ecosystem, and prevent disease. The optical biosensor with enzyme as bio-recognition elements has been an effective alternative for OPs detection. Herein, we firstly introduce various enzymes, sensing mechanisms, advantages and disadvantages used as bio-recognition elements in optical sensing for OPs detection. Then, we review various optical biosensing strategies based on enzymes as recognition elements that were ingeniously designed and successfully utilized for OPs detection, with a particular emphasis on photoluminescence (PL), chemiluminescence (CL), electrochemiluminescence (ECL), and colorimetric (CM) biosensing strategies. We not only highlight the state-of-art developments and the construction strategies of the enzyme-based optical biosensing method but also summarize the existing deficiencies, current challenges, and the future perspectives of OPs detection.

Ruthenium bipyridine complexes as electrochemiluminescent transducers for ionophore-based ion-selective detection

We report here a method to determine target ion concentrations (with Na⁺ as a model) based on ionophores and electrochemiluminescence (ECL). Ruthenium bipyridine complexes were released from thin polymeric films (plasticized poly(vinyl chloride) also containing a sodium ionophore) into the sample solution following an explicit ion-exchange process (between Na⁺ and the ruthenium complex). Two signal transducers, tris(2,2'-(pCF₃)bipyridine)ruthenium(II) (Ru(p-CF₃-bpy)₃²⁺) and tris(2,2'-bipyridyl)dichlororuthenium(II) (Ru(bpy)₃²⁺), were examined using the sensing film, with the latter providing a more sensitive detection range (ca. 1 to 100 μM) than that of the more hydrophobic one (0.01 to 1 mM). While the ionophore (Na⁺ ionophore X) offered excellent selectivity to the method, the ruthenium complexes made the measurements independent of the sample pH. Furthermore for complex biological samples such as blood serum, an indirect approach of measuring the ECL of the remaining ruthenium complexes helps avoid background matrix interference to the ECL production at the working electrode, making the ECL method more attractive for real complex samples.

Colorimetric and fluorescent turn-on detection of chloride ions with ionophore and BODIPY: Evaluation with nanospheres and cellulose paper

Here, we present the optical detection of chloride ions with co-extraction based anion-selective optodes containing a BODIPY derivative (BDP-OH) and the ionophore In(OEP)Cl. Spectroscopic studies suggested that BDP-OH and In(OEP)Cl formed an adduct BDP-O-In(OEP), which was converted to BDP-OH and In(OEP)Cl upon increasing sample Cl^- concentration, and induced signal changes in both fluorescence and absorbance modes. The method was evaluated in polystyrene-graft-poly(ethylene oxide) (PS-PEO) nanospheres (ca. 40 nm in diameter) and on cellulose paper. In contrast to Cl^- probes based on fluorescence quenching, the nanospheres exhibited turn-on fluorescence and ratiometric absorbance responses to a tunable Cl^- concentration range (10 μM-1 M). Through fluorescence microscopy, the nanospheres were able to respond to Cl^- concentration changes in HeLa cells. Cellulose paper-based Cl^- optodes with colorimetric response were successfully used to measure Cl^- in artificial sweat, providing a potential analytical tool for clinical diagnosis of cystic fibrosis.

Enhanced chemiluminescence determination of paracetamol

Due to the severe consequences of potential overdoses of paracetamol (PCM) on the human body, the measurement of PCM in pharmaceutical and biological samples is essential.

Ionophore-based pH independent detection of ions utilizing aggregation-induced effects

Ionophores have been integrated into various electrochemical and optical sensing platforms for the selective detection of ions. Previous ionophore-based optical sensors rely on a H⁺ chromoionophore as the signal transducer and consequently, suffered from a pH cross-response. pH independent methods were proposed very recently by utilizing the solvatochromic dyes or the exhaustive mode. Here, we report a pH independent sensing principle based on nanospheres containing ionophores. As the ion-exchange occurs, the signal transducer undergoes aggregation-induced emission (AIE) or aggregation-caused quenching (ACQ), leading to a dramatic change in fluorescence intensity. The principle was evaluated on different ionophores including those selective for K⁺, Na⁺, Ca²⁺, and Pb²⁺. The nanospheres were also introduced into microfluidic chips and successfully applied for the determination of sodium and potassium ion concentrations in diluted blood serum and urine samples.

Direct Visualization of Perm-Selective Ion Transportation

Perm-selective ion transportation in a nanoscale structure such as nanochannel, nanoporous membrane or nanojunction has been extensively studied with aids of nanofabrication technology for a decade. While theoretical and experimental advances pushed the phenomenon to seminal innovative applications, its basic observation has relied only on an indirect analysis such as current-voltage relation or fluorescent imaging adjacent to the nanostructures. Here we experimentally, for the first time, demonstrated a direct visualization of perm-selective ion transportation through the nanoscale space using an ionic plasma generation. A micro/nanofluidic device was employed for a micro bubble formation, plasma negation and penetration of the plasma along the nanojunction. The direct observation provided a keen evidence of perm-selectivity, i.e. allowing cationic species and rejecting anionic species. Furthermore, we can capture the plasma of lithium, which has lower mobility than sodium in aqueous state, passed the nanojunction faster than sodium due to the absence of hydrated shells around lithium. This simple, but essential visualization technique would be effective means not only for advancing the fundamental nanoscale electrokinetic study as well as interfacial ion transportation between liquid and plasma but also for providing the insight of new innovative engineering applications.

Enhancing hydrogel-based long-lasting chemiluminescence by a platinum-metal organic framework and its application in array detection of pesticides and d-amino acids

Organophosphorus pesticides (OPs) are harmful to people's health and d-amino acids (d-AAs) in the human body are closely related to various diseases. So, detection of OPs in foods and d-AAs in serum is important for food safety and clinical diagnosis. Herein, a long-lasting chemiluminescence (CL) imaging sensor was constructed for the detection of OPs and d-AAs. The method was based on N-(4-aminobutyl)-N-ethylisoluminol/Co2+/chitosan (ABEI/Co2+/CS) hydrogels, where metal organic framework materials (MOF-Pt) were selected as catalysts to improve the sensitivity greatly. Under the catalysis of acetylcholinesterase (AChE) and choline oxidase (CHO), H2O2 was produced by using acetylcholine chloride (ACh) as a substrate, which was sensitive to the proposed CL system. OPs inhibited the activity of AChE and decreased the production of H2O2, reducing CL intensity. The linear range of the method for chlorpyrifos was 0.5 ng mL-1-1.0 μg mL-1, with a limit of detection (LOD) of 0.21 ng mL-1. Seventeen kinds of OPs can be visually and simultaneously discerned by the CL imager. On the other hand, d-AAs were catalyzed and oxidized by d-α-amino oxidase (DAAO) to produce H2O2. Thus, d-Ala in serum was used as a model to be detected by the proposed method. The linear range for d-Ala was 1.0 μM-10 mM, with an LOD of 0.12 μM.