Insertable Fast-Response Amperometric NO/CO Dual Microsensor: Study of Neurovascular Coupling During Acutely Induced Seizures of Rat Brain Cortex

Electrochemical Detection of Gasotransmitters: Status and Roadmap

Gasotransmitters, including nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S), are a class of gaseous, endogenous signaling molecules that interact with one another in the regulation of critical cardiovascular, immune, and neurological processes. The development of analytical sensing mechanisms for gasotransmitters, especially multianalyte mechanisms, holds vast importance and constitutes a growing area of study. This review provides an overview of electrochemical sensing mechanisms with an emphasis on opportunities in multianalyte sensing. Electrochemical methods demonstrate good sensitivity, adequate selectivity, and the most well-developed potential for the multianalyte detection of gasotransmitters. Future research will likely address challenges with sensor stability and biocompatibility (i.e., sensor lifetime and cytotoxicity), sensor miniaturization, and multianalyte detection in biological settings.

High-Performance Recognition, Cell-Imaging, and Efficient Removal of Carbon Monoxide toward a Palladium-Mediated Fluorescent Sensing Platform

Novel high-performance fluorescent approaches have always significant demand for room-temperature detection of carbon monoxide (CO), which is highly toxic even at low concentration levels and is not easy to recognize due to its colorless and odorless nature. In this paper, we constructed a palladium-mediated fluorescence turn-on sensing platform (TPANN-Pd) for the recognition of CO at room temperature, revealing simultaneously quick response speed (<30 s), excellent selectivity, superior sensitivity, and low detection limit (∼160 nM for CORM-3, ∼1.7 ppb for CO vapor). Moreover, rapid detection and efficient removal (24%) from the air by naked-eye vision has been successfully realized based on TPANN-Pd supramolecular gels. Furthermore, the developed sensing platform was elucidated with low cytotoxicity and high cellular uptake, and it was successfully applied to CO imaging in living cells, providing real-time monitoring of potential CO-involved reactions in biological systems.

Sensitive and effective imaging of carbon monoxide in living systems with a near-infrared fluorescent probe

CO, a gas molecule that is harmful to living organisms, has a high affinity with hemoglobin, which will cause severe hypoxia. However, in recent years, researchers have discovered that endogenous CO, similar to NO, is one of the messenger molecules, which has a certain regulatory effect in many physiological and pathological processes in the respiratory system, cardiovascular system, and nervous system. Therefore, it is urgent to explore an effective method to monitor the role of CO under physiological and pathological conditions. Herein, we designed and synthesized a near-infrared small-molecule fluorescent probe for the detection of CO in living cells. In this design, a two-site BODIPY dye was introduced as the fluorophore, and the allyl chloroformate part as the CO reactive group. The probe displays excellent sensitivity, selectivity, and a good linear relationship to CO. Furthermore, it shows good biocompatibility and low cytotoxicity. This probe has been successfully applied to the detection of CO in a variety of cells. The developed fluorescent probe can serve as a potential molecular imaging tool for in vivo imaging and detection of CO.

A turn-on homodimer fluorescent probe based on homo-FRET for the sensing of biothiols in lysosome: a trial of a new turn-on strategy

Fluorescence resonance energy transfer (FRET) is often applied to construct fluorescent probes for acquiring high selectivity and sensitivity. According to the FRET theory, a homodimer composed of two identical fluorophores with a small Stokes shift has only weak fluorescence due to homo-FRET between fluorophores, and the fluorescence could be recovered after the destruction of the homodimer. In this study, we designed and synthesized a homodimer fluorescent probe, namely 1,3,5,7-tetramethyl-8-(4'-phenylthiophenol)-boron difluoride-dipyrrole methane dimer (D-TMSPB), based on this turn-on strategy. In D-TMSPB, the disulfide moiety was selected as the response moiety of biothiols, and BODIPY fluorophore was chosen as both donor and acceptor in FRET due to the ultra-small Stokes shifts and obvious overlap of its excitation/emission peak. D-TMSPB exhibited only weak fluorescence. After selective reaction with biothiols, FRET was destroyed and the derivative exhibited strong fluorescence at 514 nm with the limit of detection of about 0.15 μM for GSH. Notably, the derivative of biothiols shows remarkable fluorescence only in acidic conditions, which accords with the internal environment of lysosome. Thus, D-TMSPB was applied to image the biothiols of lysosome in living cells. The turn-on fluorescence of D-TMSPB indicated that homo-FRET is a practical strategy to design turn-on fluorescent probes, particularly for the sensing mechanism based on leaving groups.

Injectable Biomedical Devices for Sensing and Stimulating Internal Body Organs

The rapid pace of progress in implantable electronics driven by novel technology has created devices with unconventional designs and features to reduce invasiveness and establish new sensing and stimulating techniques. Among the designs, injectable forms of biomedical electronics are explored for accurate and safe targeting of deep-seated body organs. Here, the classes of biomedical electronics and tools that have high aspect ratio structures designed to be injected or inserted into internal organs for minimally invasive monitoring and therapy are reviewed. Compared with devices in bulky or planar formats, the long shaft-like forms of implantable devices are easily placed in the organs with minimized outward protrusions via injection or insertion processes. Adding flexibility to the devices also enables effortless insertions through complex biological cavities, such as the cochlea, and enhances chronic reliability by complying with natural body movements, such as the heartbeat. Diverse types of such injectable implants developed for different organs are reviewed and the electronic, optoelectronic, piezoelectric, and microfluidic devices that enable stimulations and measurements of site-specific regions in the body are discussed. Noninvasive penetration strategies to deliver the miniscule devices are also considered. Finally, the challenges and future directions associated with deep body biomedical electronics are explained.

Electrochemical Nitric Oxide Microsensors Based on a Fluorinated Xerogel Screening Layer for in Vivo Brain Monitoring

Nitric oxide (NO) is an important free radical synthesized and released by brain cells. At low (nanomolar) levels, it modulates synaptic transmission and neuronal activity, but at much higher levels mediates neuronal injury through oxidative stress. However, the precise concentrations at which these biological actions are exerted are still poorly defined. Electrochemical detection of NO in vivo requires rigorous exclusion of endogenous redox molecules such as ascorbate or nitrite. A fluorinated xerogel composed of trimethoxymethylsilane and heptadecafluoro-1,1,2,2-tetrahydrodecyl silane has been proposed to create a screening layer around NO sensors, protecting against such chemical interference in vitro. Here we detected NO in the living brain using carbon fiber microelectrodes covered with nickel porphyrin and this fluorinated xerogel. These microsensors were insensitive to interfering redox molecules and surpassed similar microelectrodes coated with a Nafion screening layer. In vivo, in the rat parietal cortex, these electrodes could detect brain NO released by local microinjection of the glutamatergic agonist N-methyl-d-aspartate (NMDA). NMDA-evoked NO release peaked at 1.1 μM and lasted more than 20 min. This fluorinated xerogel screening layer can therefore be applied in vivo, allowing for the fabrication of highly specific microsensors to study NO physio-pathological actions in the brain.

A review of the actions of Nitric Oxide in development and neuronal function in major invertebrate model systems

Ever since the late-eighties when endothelium-derived relaxing factor was found to be the gas nitric oxide, endogenous nitric oxide production has been observed in virtually all animal groups tested and additionally in plants, diatoms, slime molds and bacteria. The fact that this new messenger was actually a gas and therefore didn't obey the established rules of neurotransmission made it even more intriguing. In just 30 years there is now too much information for useful comprehensive reviews even if limited to animals alone. Therefore this review attempts to survey the actions of nitric oxide on development and neuronal function in selected major invertebrate models only so allowing some detailed discussion but still covering most of the primary references. Invertebrate model systems have some very useful advantages over more expensive and demanding animal models such as large, easily identifiable neurons and simple circuits in tissues that are typically far easier to keep viable. A table summarizing this information along with the major relevant references has been included for convenience.

A fluorescent probe for carbon monoxide based on allyl ether rather than allyl ester: A practical strategy to avoid the interference of esterase in cell imaging

Pd⁰-mediated Tsuji-Trost reaction is a practical strategy to design fluorescent probes for carbon monoxide (CO) sensing, and in such reaction CO can reduce Pd²⁺ to Pd⁰ in-situ and remove allyl groups on fluorophores. In most of these probes, esters are commonly used to link allyl on fluorophores. We found that the ester groups could be hydrolyzed by esterase activity of fetal bovine serum (FBS), while FBS is a requisite in cell culture, and the hydrolysis could interfere the Pd⁰-mediated Tsuji-Trost reaction. In this study, we synthesized a fluorescent probe (Cou-CO) using allyl ether as reaction site rather than allyl ester. Cou-CO is non-fluorescence, and could react with CO under the presence of Pd⁰ to form Cou with strong fluorescence, and the maximum excitation and emission wavelengths of Cou are 464 nm and 495 nm respectively. Cou-CO shows excellent selectivity to CO and could avoid the effect of FBS with the limit of detection for CO is 78 nm. Finally, Cou-CO was successfully applied for imaging of CO in living cells.

Selectivity enhancement of amperometric nitric oxide detection via shape-controlled electrodeposition of platinum nanostructures

Nitric oxide (NO) is a biologically multifunctional gaseous signaling molecule. For electrochemical NO detections, complex membranes are commonly adopted to acquire the selectivity for NO over other oxidizable biological species. In this study, we demonstrate the improved selectivity in amperometric NO measurements at nanostructured Pt. The Pt layers were electrodeposited on Au substrate electrodes at a constant potential (-0.2 V vs. Ag/AgCl) with a constant deposition charge (0.08 C). The various distinctive nanostructures of Pt deposits were obtained via either changing the precursor concentrations (from 5 to 75 mM K2PtCl4) or using a different precursor (75 mM H2PtCl6). With a higher K2PtCl4 concentration, the Pt deposition became less sharp and the smoothest Pt was deposited with 75 mM H2PtCl6. The most greatly sharp-pointed nanostructures were generated with the lowest precursor concentration (5 mM K2PtCl4) and exhibited the highest sensitivity, which was attributed to the hydrophobic property of sharply nanostructured Pt. A hydrophobic neutral gas molecule, NO, possibly has a more favorable access to the inner surface of more hydrophobic Pt deposition and eventually increases the oxidation current. NO current sensitivity was enhanced at the more hydrophobic Pt surface, whereas the oxidation currents of acetaminophen, l-ascorbic acid, nitrite and hydrogen peroxide, four oxidizable biological interfering species, were independent of the Pt nanostructure. Conclusively, the enhanced amperometric selectivity to NO was achieved by the simple electrodeposition method without any additional membranes.

Fabrication of a Flexible and Stretchable Nanostructured Gold Electrode Using a Facile Ultraviolet-Irradiation Approach for the Detection of Nitric Oxide Released from Cells

We developed a simple and environmentally friendly ultraviolet (UV)-irradiation-assisted technique to fabricate a stretchable, nanostructured gold film as a flexible electrode for the detection of NO release. The flexible gold film endows the electrode with desirable electrochemical stability against mechanical deformation, including bending to different curvatures and bearing repeated bending circumstances (200 times). The flexible nanostructured gold electrodes can catalyze NO oxidation at 0.85 V (as opposed to Ag/AgCl) and detect NO within a wide linearity in the range of 10 nM to 1.295 μM. Its excellent NO-sensing ability and its stretchability together with its biocompatibility allows the electrode to electrochemically monitor NO release from mechanically sensitive HUVECs in both their unstretched and stretched states. This result paves the way for an effective and easily accessible platform for designing stretchable and flexible electrodes and opens more opportunities for sensing chemical-signal molecules released from cells or other biological samples during mechanical stimulation.

Insertable NO/CO Microsensors Recording Gaseous Vasomodulators Reflecting Differential Neuronal Activation Level with Respect to Seizure Focus

Nitric oxide (NO) and carbon monoxide (CO) are important signaling molecules shaping vasomodulation. This paper reports simultaneous in vivo monitoring of NO, CO and dendritic summation of action potential at three different cortical regions: seizure focus and two additional places, vertically and horizontally separated by 1.2 mm from the seizure focus, during epileptic seizure induced by 4-aminopyrindine injection. An amperometric dual microsensor having a high spatiotemporal resolution monitored fast and dynamic changes of NO and CO, and neural changes were recorded with a glass pipet electrode for local field potential (LFP). At all three locations, onsets and offsets of NO and CO changes well synchronized with fast LFP changes, while the patterns and concentrations of NO and CO changes were varied depending on the sensing locations. The insertable NO/CO dual microsensor was successful to measure intimately linked NO and CO in acute seizure events with high sensitivity, selectivity, and spatiotemporal resolution.

Amperometric Microsensors Monitoring Glutamate-Evoked In Situ Responses of Nitric Oxide and Carbon Monoxide from Live Human Neuroblastoma Cells

In the brain, nitric oxide (NO) and carbon monoxide (CO) are important signaling gases which have multifaceted roles, such as neurotransmitters, neuromodulators, and vasodilators. Even though it is difficult to measure NO and CO in a living system due to their high diffusibility and extremely low release levels, electrochemical sensors are promising tools to measure in vivo and in vitro NO and CO gases. In this paper, using amperometric dual and septuple NO/CO microsensors, real-time NO and CO changes evoked by glutamate were monitored simultaneously for human neuroblastoma (SH-SY5Y) cells. In cultures, the cells were differentiated and matured into functional neurons by retinoic acid and brain-derived neurotrophic factor. When glutamate was administrated to the cells, both NO and CO increases and subsequent decreases returning to the basal levels were observed with a dual NO/CO microsensor. In order to facilitate sensor’s measurement, a flower-type septuple NO/CO microsensor was newly developed and confirmed in terms of the sensitivity and selectivity. The septuple microsensor was employed for the measurements of NO and CO changes as a function of distances from the position of glutamate injection. Our sensor measurements revealed that only functionally differentiated cells responded to glutamate and released NO and CO.