Miniaturized Implantable Fluorescence Probes Integrated with Metal-Organic Frameworks for Deep Brain Dopamine Sensing

Continuously monitoring neurotransmitter dynamics can offer profound insights into neural mechanisms and the etiology of neurological diseases. Here, we present a miniaturized implantable fluorescence probe integrated with metal-organic frameworks (MOFs) for deep brain dopamine sensing. The probe is assembled from physically thinned light-emitting diodes (LEDs) and phototransistors, along with functional surface coatings, resulting in a total thickness of 120 μm. A fluorescent MOF that specifically binds dopamine is introduced, enabling a highly sensitive dopamine measurement with a detection limit of 79.9 nM. A compact wireless circuit weighing only 0.85 g is also developed and interfaced with the probe, which was later applied to continuously monitor real-time dopamine levels during deep brain stimulation in rats, providing critical information on neurotransmitter dynamics. Cytotoxicity tests and immunofluorescence analysis further suggest a favorable biocompatibility of the probe for implantable applications. This work presents fundamental principles and techniques for integrating fluorescent MOFs and flexible electronics for brain-computer interfaces and may provide more customized platforms for applications in neuroscience, disease tracing, and smart diagnostics.

Bimetallic Biogenic Pt-Ag Nanoparticle and Their Application for Electrochemical Dopamine Sensor

In this study, Silver-Platinum (Pt-Ag) bimetallic nanoparticles were synthesized by the biogenic reduction method using plant extracts. This reduction method offers a highly innovative model for obtaining nanostructures using fewer chemicals. According to this method, a structure with an ideal size of 2.31 nm was obtained according to the Transmission Electron Microscopy (TEM) result. The Pt-Ag bimetallic nanoparticles were characterized using Fourier Transform Infrared Spectroscopy (FTIR), X-ray Diffractometry (XRD), and Ultraviolet-Visible (UV-VIS) spectroscopy. For the electrochemical activity of the obtained nanoparticles in the dopamine sensor, electrochemical measurements were made with the Cyclic Voltammetry (CV) and Differential Pulse Voltammetry (DPV) methods. According to the results of the CV measurements taken, the limit of detection (LOD) was 0.03 µM and the limit of quantification (LOQ) was 0.11 µM. To investigate the antibacterial properties of the obtained Pt-Ag NPs, their antibacterial effects on Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) bacteria were investigated. In this study, it was observed that Pt-Ag NPs, which were successfully synthesized by biogenic synthesis using plant extract, exhibited high electrocatalytic performance and good antibacterial properties in the determination of dopamine (DA).

A Recognition-Molecule-Free Photoelectrochemical Sensor Based on Ti3C2/TiO2 Heterostructure for Monitoring of Dopamine

Herein, a novel, recognition-molecule-free electrode based on Ti₃C₂/TiO₂ composites was synthesized using Ti₃C₂ as the Ti source and TiO₂ in situ formed by oxidation on the Ti₃C₂ surface for the selective detection of dopamine (DA). The TiO₂ in situ formed by oxidation on the Ti₃C₂ surface not only increased the catalytically active surface for DA binding but also accelerated the carrier transfer due to the coupling between TiO₂ and Ti₃C₂, resulting in a better photoelectric response than pure TiO₂. Through a series of experimental conditions optimization, the photocurrent signals obtained by the MT100 electrode were proportional to the DA concentration from 0.125 to 400 µM, with a detection limit estimated at 0.045 µM. We also monitored DA in human blood serum samples using the MT100 electrode. The results showed good recovery, demonstrating the promising use of the sensor for the analysis of DA in real samples.

Surface-Activated Pencil Graphite Electrode for Dopamine Sensor Applications: A Critical Review

Pencil graphite electrode (PGE) is an alternative, commercially available, ready-to-use, screen-printed electrode for a wide range of electroanalytical applications. Due to the complex-matrix composition and unpredictable electro-inactive nature of PGE in its native form, a surface pre-treatment/activation procedure is highly preferred for using it as an electroactive working electrode for electroanalytical applications. In this article, we review various surface pre-treatment and modification procedures adopted in the literature with respect to the sensitive and selective detection of dopamine as a model system. Specific generation of the carbon-oxygen functional group, along with partial surface exfoliation of PGE, has been referred to as a key step for the activation. Based on the Scopus^® index, the literature collection was searched with the keywords "pencil and dopamine". The obtained data were segregated into three main headings as: (i) electrochemically pre-treated PGE; (ii) polymer-modified PGEs; and (iii) metal and metal nanocomposite-modified PGE. This critical review covers various surface activation procedures adopted for the activation for PGE suitable for dopamine electroanalytical application.

Cyclophosphazene Intrinsically Derived Heteroatom (S, N, P, O)-Doped Carbon Nanoplates for Ultrasensitive Monitoring of Dopamine from Chicken Samples

A novel, metal-free electrode based on heteroatom (S, N, P, O)-doped carbon nanoplates (SNPO-CPL) modifying lead pencil graphite (LPG) has been synthesized by carbonizing a unique heteroatom (S, N, P, O)-containing novel polymer, poly(cyclcotriphosphazene-co-2,5-dioxy-1,4-dithiane) (PCD), for precise screening of dopamine (DA). The designed electrode, SNPO-CPL-800, with optimized percentage of S, N, P, O doping through the sp2-carbon chain, and a large number of surface defects (thus leading to a maximum exposition number of catalytic active sites) led to fast molecular diffusion through the micro-porous structure and facilitated strong binding interaction with the targeted molecules in the interactive signaling transducer at the electrode-electrolyte interface. The designed SNPO-CPL-800 electrode exhibited a sensitive and selective response towards DA monitoring, with a limit of detection (LOD) of 0.01 nM. We also monitored DA levels in commercially available chicken samples using the SNPO-CPL-800 electrode even in the presence of interfering species, thus proving the effectiveness of the designed electrode for the precise monitoring of DA in real samples. This research shows there is a strong potential for opening new windows for ultrasensitive DA monitoring with metal-free electrodes.

Heterostructured ZnCdS@ZIF-67 as a Photocatalyst for Fluorescent Dye Degradation and Selectively Nonenzymatic Sensing of Dopamine

Dopamine (DA) plays the role of the transmitter of information in the brain. Neurological diseases and depression are in close relationship with DA release. In this study, we developed a co-catalyst Zn_0.2Cd_0.8S@zeolitic imidazolate framework-67 (Zn_0.2Cd_0.8S@ZIF-67) to improve the photocatalyst efficacy of Rhodamine B (RhB) and electrochemical sensing of DA. Results show that Zn_0.2Cd_0.8S@ZIF-67 exhibits optimal photocatalytic activity with the addition of 80 mg ZIF-67. The degradation percentage of RhB by Zn_0.2Cd_0.8S@ZIF-67 reached 98.40% when the co-catalyst was 50 mg. Radical trapping experiments show that ·O₂^- played a significant role in the photocatalytic degradation of RhB. The catalytic mechanism of the Zn_0.2Cd_0.8S@ZIF-67 was found as a Z-type photocatalysis. Finally, a DA biosensor was constructed and displayed a high response and selectivity to DA. This can be attributed to the heterojunction between Zn_0.2Cd_0.8S and ZIF-67, which can significantly enhance the separation of e^-/h⁺ and improve charge transfer. These findings will play a positive role in the in-situ monitoring of neurological diseases and depression.

Age-dependent alterations in key components of the nigrostriatal dopaminergic system and distinct motor phenotypes

The nigrostriatal dopaminergic (DA) system, which includes DA neurons in the ventral and dorsal tiers of the substantia nigra pars compacta (vSNc, dSNc) and DA terminals in the dorsal striatum, is critically implicated in motor control. Accumulating studies demonstrate that both the nigrostriatal DA system and motor function are impaired in aged subjects. However, it is unknown whether dSNc and vSNc DA neurons and striatal DA terminals age in similar patterns, and whether these changes parallel motor deficits. To address this, we performed ex vivo patch-clamp recordings in dSNc and vSNc DA neurons, measured striatal dopamine release, and analyzed motor behaviors in rodents. Spontaneous firing in dSNc and vSNc DA neurons and depolarization-evoked firing in dSNc DA neurons showed inverse V-shaped changes with age. But depolarization-evoked firing in vSNc DA neurons increased with age. In the dorsal striatum, dopamine release declined with age. In locomotor tests, 12-month-old rodents showed hyperactive exploration, relative to 6- and 24-month-old rodents. Additionally, aged rodents showed significant deficits in coordination. Elevating dopamine levels with a dopamine transporter inhibitor improved both locomotion and coordination. Therefore, key components in the nigrostriatal DA system exhibit distinct aging patterns and may contribute to age-related alterations in locomotion and coordination.

Ventral pallidum DRD3 potentiates a pallido-habenular circuit driving accumbal dopamine release and cocaine seeking

Drugs of abuse induce persistent remodeling of reward circuit function, a process thought to underlie the emergence of drug craving and relapse to drug use. However, how circuit-specific, drug-induced molecular and cellular plasticity can have distributed effects on the mesolimbic dopamine reward system to facilitate relapse to drug use is not fully elucidated. Here, we demonstrate that dopamine receptor D3 (DRD3)-dependent plasticity in the ventral pallidum (VP) drives potentiation of dopamine release in the nucleus accumbens during relapse to cocaine seeking after abstinence. We show that two distinct VP DRD3+ neuronal populations projecting to either the lateral habenula (LHb) or the ventral tegmental area (VTA) display different patterns of activity during drug seeking following abstinence from cocaine self-administration and that selective suppression of elevated activity or DRD3 signaling in the LHb-projecting population reduces drug seeking. Together, our results uncover how circuit-specific DRD3-mediated plasticity contributes to the process of drug relapse.

The chemical tools for imaging dopamine release

Dopamine is a modulatory neurotransmitter involved in learning, motor functions, and reward. Many neuropsychiatric disorders, including Parkinson's disease, autism, and schizophrenia, are associated with imbalances or dysfunction in the dopaminergic system. Yet, our understanding of these pervasive public health issues is limited by our ability to effectively image dopamine in humans, which has long been a goal for chemists and neuroscientists. The last two decades have witnessed the development of many molecules used to trace dopamine. We review the small molecules, nanoparticles, and protein sensors used with fluorescent microscopy/photometry, MRI, and PET that shape dopamine research today. None of these tools observe dopamine itself, but instead harness the biology of the dopamine system-its synthetic and metabolic pathways, synaptic vesicle cycle, and receptors-in elegant ways. Their advantages and weaknesses are covered here, along with recent examples and the chemistry and biology that allow them to function.

Green synthesis of nonprecious metal-doped copper hydroxide nanoparticles for construction of a dopamine sensor

Background: Copper oxide nanoparticles doped with nonprecious metal species (Ni and Mn) were synthesized. Method: A glassy carbon electrode (GCE) was modified by drop-casting of nanostructure suspensions, constructing Ni:Cu(OH)₂/GCE, Mn:Cu(OH)₂/GCE and Cu(OH)₂/GCE. Results: The voltammetric oxidation of dopamine (DA) by the constructed electrodes confirmed that the electrocatalytic oxidation of DA is a reversible, pH-dependent, diffusion-controlled process; the best response was obtained by Mn:Cu(OH)₂/GCE. A sensitive calibration graph (0.664 μA/μM) was produced for DA in the concentration range of 0.3-10.0 μM, with a detection limit of 79 nM using Mn:Cu(OH)₂/GCE. Conclusion: The Mn:Cu(OH)₂/GCE possessed an accurate response toward DA with an acceptable selectivity, stability and antifouling effect, revealing the applicability of the Mn:Cu(OH)₂/GCE for DA analysis in biological samples.

AC Measurements Using Organic Electrochemical Transistors for Accurate Sensing

Organic electrochemical transistors (OECTs) have been successfully employed for a variety of applications , especially chemical and biological sensing. Although the device response to analytes can be directly monitored by measuring steady-state channel currents of the devices, it is challenging to obtain stable signals with high signal-to-noise ratios. In this work, we developed a novel method for electrochemical sensing by measuring both the transconductance and the phase of the AC channel current for the first time. Then we successfully realized highly sensitive ion strength sensors and dopamine sensors based on the AC method. Our results indicate that the AC method is more sensitive than typical DC methods and can provide more stable data in sensing applications. Considering that the sensors can be conveniently integrated with AC circuits, this technology is expected to find broad applications in the future.

Human Dopamine Receptor-Conjugated Multidimensional Conducting Polymer Nanofiber Membrane for Dopamine Detection

In the brain and central nervous system, dopamine plays a crucial role as a neurotransmitter or a local chemical messenger for interneuronal communication. Dopamine is associated with renal, hormonal, and cardiovascular systems. Additionally, dopamine dysfunction is known to cause serious illnesses, such as Parkinson's disease and Alzheimer's disease. Therefore, dopamine detection is essential for medical diagnosis and disease prevention and requires a novel strategy with high sensitivity and selectivity and a rapid response. Herein, we present a novel human dopamine receptor (hDRD1)-conjugated multidimensional conducting polymer nanofiber (NF) membrane for the selective and sensitive detection of dopamine. The membrane, which consists of multidimensional carboxylated poly(3,4-ethylenedioxythiophene) (MCPEDOT) NFs with nanorods, is used as a transistor in a liquid-ion gated field-effect transistor (FET)-based biosensor. Interestingly, hDRD1 is first expressed in Escherichia coli before it is immobilized onto the MCPEDOT NF. The hDRD1-MCPEDOT NF-based FET exhibits a rapid real-time response (<2 s) with high dopamine selectivity and sensitivity performance (approximately 100 fM). Furthermore, this FET device can be integrated into a poly(dimethylsiloxane)-based microfluidic system and also can retain its high performance in the integrated system, which results in the generation of large-scale dopamine biosensors with a novel geometry.