Three-Input Logic Gates with Potential Applications for Neuronal Imaging

Imaging Neurotransmitters with Small-Molecule Fluorescent Probes

Neurotransmitters play a crucial role in regulating communication between neurons within the brain and central nervous system. Thus, imaging neurotransmitters has become a high priority in neuroscience. This minireview focuses on recent advancements in the development of fluorescent small-molecule fluorescent probes for neurotransmitter imaging and applications of these probes in neuroscience. Innovative approaches for probe design are highlighted as well as attributes which are necessary for practical utility, with a view to inspiring new probe development capable of visualizing neurotransmitters.

Lab-on-a-molecule and multi-analyte sensing

The concept of a lab-on-a-molecule, which was proposed just short of two decades ago, has captured the imagination of scientists. From originally being proposed as an AND logic gate driven by three chemical inputs as a direct way of detecting congregations of chemical species, the definition of what constitutes a lab-on-a-molecule has broadened over the years. In this review, molecules that can detect multiple analytes by fluorescence, among other techniques, are reviewed and discussed, in the context of molecular logic and multi-analyte sensing. The review highlights challenges and suggestions for moving the frontiers of research in this field to the next dimension.

Synthesis of a Near-Infrared Fluorescent Probe for Imaging Catecholamines via a Tandem Nucleophilic Aromatic Substitution

A near-infrared (NIR) fluorescent probe NS667 was developed using a novel synthetic strategy by integrating an electron-rich 1,2,3,4-tetrahydroquinoxaline (THQ) into the scaffold from NS510, which binds to catecholamines with high affinity. The fluorophore core was constructed with a tandem nucleophilic aromatic substitution. Upon binding to catecholamines, the fluorescence of this probe shifted, with the emission in the NIR region. Live cell imaging results demonstrate that NS667 can effectively image norepinephrine in chromaffin cells with shifted fluorescence, which highlights the potential of the probe for neuroimaging in tissues.

3-Input AND Molecular Logic Gate with Enhanced Fluorescence Output: The Key Atom for the Accurate Prediction of the Spectra

The development of artificial receptors for sensing and recognition of species, as well as for advanced logic functions, is a significant challenge in the field of molecular information technology. Here, we study theoretically, via DFT/TD-DFT calculations, the photophysical properties of a 3-input AND molecular logic gate which presents an enhanced fluorescence spectrum. It was found that the geometry conformation at an N atom of the piperazine group is the key factor for the correct calculation of the absorption spectra of the calculated structures. Its geometry is between tetrahedral and planar, while changes in the corresponding CNCC dihedral angle of about 10 degrees can cause significant shifts of the main peak of the absorption spectra up to 100 nm. Moreover, the unusually enhanced fluorescence of a molecular logic gate (MLG) is explained. Finally, we conclude that molecular systems having N atoms, whose geometry is between planar and tetrahedral, can be ideal molecules as sensors and molecular logic gates. Our calculated absorption and emission spectra are in excellent agreement with available experimental data.

A Bioluminescent Probe for Detecting Norepinephrine in Vivo

As a neurotransmitter, norepinephrine (NE) is critical for psychiatric conditions, neurodegenerative diseases, and pheochromocytoma. A real-time and noninvasive method for the detection of NE as a tracer to investigate the NE-relevant disease treatment process is urgently desirable. Herein, we successfully developed a turn-on NE bioluminescent probe (NBP), which was grounded on p-toluenethiol deprotectrf by nucleophilic substitution. Compared with other analytes, the NBP exhibited high sensitivity and selectivity in vitro. More importantly, the NBP provides a promising strategy for in vivo imaging of NE in living animals with noninvasive visualization and real-time features.

A ratiometric fluorescence sensor for ascorbic acid determination based on an AND-NAND logic pair

An AND-NAND logic pair is reported based on non-purified carbon quantum dots (CDs) for ascorbic acid (AA) detection. In the logic operation, molybdenum oxide nanosheets (MoO3 NSs) and AA are used as two signal inputs. In the presence of AA, MoO3 NSs are reduced to plasmonic molybdenum oxide, which decreases the CD fluorescence intensity because of a static quenching, dynamic quenching, and internal filtration effect. Meanwhile, the AA is oxidized to dehydroascorbic acid and forms fluorescent 3-(dihydroxyethyl) furo [3,4-b] quinoxaline-1-one with o-phenylenediamine from non-purified CDs. On this basis, an AND-NAND logic pair was constructed and used as a ratiometric fluorescence sensor for highly sensitive detection of AA. The method has a wide linear range of 0.05-50 μM, and a detection limit of 34 nM. In addition, it was used to detect AA in fresh fruit. Potential applications include chemical computing, optoelectronic devices, biomedical science, and environmental monitoring. HIGHLIGHTS: 1. A ratiometric fluorescence sensor based on AND-NAND logic pair constructed by CDs and MoO3 NSs was successfully fabricated. 2. The ratiometric fluorescence sensor exhibited satisfactory linear range, high sensitivity, and good selectivity for AA. 3. The ratiometric fluorescence method was able to detect AA in fresh fruit with good results comparable to official fluorescence methods.

Sub-nanomolar sensitive GZnP3 reveals TRPML1-mediated neuronal Zn2+ signals

Although numerous fluorescent Zn²⁺ sensors have been reported, it is unclear whether and how Zn²⁺ can be released from the intracellular compartments into the cytosol due to a lack of probes that can detect physiological dynamics of cytosolic Zn²⁺. Here, we create a genetically encoded sensor, GZnP3, which demonstrates unprecedented sensitivity for Zn²⁺ at sub-nanomolar concentrations. Using GZnP3 as well as GZnP3-derived vesicular targeted probes, we provide the first direct evidence that Zn²⁺ can be released from endolysosomal vesicles to the cytosol in primary hippocampal neurons through the TRPML1 channel. Such TRPML1-mediated Zn²⁺ signals are distinct from Ca²⁺ in that they are selectively present in neurons, sustain longer, and are significantly higher in neurites as compared to the soma. Together, our work not only creates highly sensitive probes for investigating sub-nanomolar Zn²⁺ dynamics, but also reveals new pools of Zn²⁺ signals that can play critical roles in neuronal function.

Numerous fluorescent Zn²⁺ sensors are available but most are unsuitable to detect physiological dynamics of cytosolic Zn²⁺. In this study, the authors present a genetically encoded sensor with sub-nanomolar sensitivity and show that Zn^2 + is released from endolysosomal vesicles via TRPML1 in neurons.

Quantum chemical elucidation of the turn-on luminescence mechanism in two new Schiff bases as selective chemosensors of Zn2+: synthesis, theory and bioimaging applications

We report the synthesis and characterization of two new selective zinc sensors (S,E)-11-amino-8-((2,4-di-tert-butyl-1-hydroxybenzylidene) amino)-11-oxopentanoic acid (A) and (S,E)-11-amino-8-((8-hydroxybenzylidene)amino)-11-oxopentanoic acid (B) based on a Schiff base and an amino acid. The fluorescent probes, after binding to Zn2+ ions, presented an enhancement in fluorescent emission intensity up to 30 times (ϕ = A 50.10 and B 18.14%). The estimated LOD for compounds A and B was 1.17 and 1.20 μM respectively (mixture of acetonitrile : water 1 : 1). Theoretical research has enabled us to rationalize the behaviours of the two selective sensors to Zn2+ synthesized in this work. Our results showed that in the free sensors, PET and ESIPT are responsible for the quenching of the luminescence and that the turn-on of luminescence upon coordination to Zn2+ is mainly induced by the elimination of the PET, which is deeply analysed through EDA, NOCV, molecular structures, excited states and electronic transitions via TD-DFT computations. Confocal fluorescence microscopy experiments demonstrate that compound A could be used as a fluorescent probe for Zn2+ in living cells.

Doping Dopamine in Carbon Nanoparticles: A New Multifunctional Logic-Based Decision-Making Molecule

A dopamine-functionalized carbon nanoparticle (CNP)-based platform is designed to reversibly control the optical signal, leading to a multifunctional logic system regulated by pH and light. pH-regulated unique reversible transformation of oxidized and reduced forms of a neurotransmitter, dopamine, conjugated with CNPs plays a decisive role in capturing the final output of the logic function. Inspired by this phenomenon, herein, we report the use of dopamine-docked CNPs to construct different molecular logic gates with an intention to develop the next-generation molecular logic gates. We could successfully construct two basic molecular logic gates, namely, YES and NOT, using one input; two modular logic gates; an IMPLICATION logic gate using two inputs; and finally a combination of OR and AND gates using three inputs. The optical response of the synthesized NP conjugate provides a fluorescence-based "Erase-Read-Write-Read" function. The proposed phenomenon may open a new concept of biochemical logic gates with fluorescence output for neuronal imaging.

Molecular memory with downstream logic processing exemplified by switchable and self-indicating guest capture and release

Molecular-logic based computation (MLBC) has grown by accumulating many examples of combinational logic gates and a few sequential variants. In spite of many inspirations being available in biology, there are virtually no examples of MLBC in chemistry where sequential and combinational operations are integrated. Here we report a simple alcohol-ketone redox interconversion which switches a macrocycle between a large or small cavity, with erect aromatic walls which create a deep hydrophobic space or with collapsed walls respectively. Small aromatic guests can be captured or released in an all or none manner upon chemical command. During capture, the fluorescence of the alcohol macrocycle is quenched via fluorescent photoinduced electron transfer switching, meaning that its occupancy state is self-indicated. This represents a chemically-driven RS Flip-Flop, one of whose outputs is fed into an INHIBIT gate. Processing of outputs from memory stores is seen in the injection of packaged neurotransmitters into synaptic clefts for onward neural signalling. Overall, capture-release phenomena from discrete supermolecules now have a Boolean basis.

Nanoscale fluorescent metal-organic framework composites as a logic platform for potential diagnosis of asthma

Asthma is a common chronic disorder, and the decreased hydrogen sulfide (H₂S) production in the lung has been considered as an early detection biomarker for asthma. However, the detection of H₂S in biological systems remains a challenge; because it requires the designed sensors to have the following features: nanoscale size, good biocompatibility, real-time detection, high selectivity/sensitivity, and good water stability. Here, we propose the potential of using nanoscale fluorescent metal-organic framework (MOF) composites Eu³⁺/Ag⁺@UiO-66-(COOH)₂ (hereafter denoted as EAUC) as a logic platform for tentative diagnosis of asthma by detecting the biomarker H₂S. This INHIBIT logic gate based on Eu³⁺@UiO-66-(COOH)₂ (EUC) can be produced by choosing Ag⁺ and H₂S as inputs and by monitoring the fluorescent signal (I₆₁₅) as an output. Our fluorescent studies indicate that the EAUC exhibits excellent selectivity, extreme sensitivity (limit of detection: 23.53 μM), and real-time in situ detection of H₂S. Further, MTT analysis in PC12 cells shows that the EAUC possesses low cytotoxicity and favourable biocompatibility that are suitable for the detection of biomarker H₂S in vivo, as demonstrated by the successful detection of spiked H₂S in the diluted serum samples. This work represents the possibility of using MOF-based logic platform for tentative diagnosis of asthma in clinical medicine.

Imaging dynamic changes of an intracellular cysteine pool that responds to the stimulation of external oxidative stress

A fluorescence-based probe (CyP) suitable for imaging the dynamic changes of endogenous cysteine activities under external oxidative stress in living cells, nematode, and Arabidopsis thaliana was developed.

A selective fluorescent probe for relay detection of Zn2+ and tartrate: Application to logic circuit and living cell imaging

A novel fluorescent probe 2-(2'-hydroxyphenyl)-4-(phenylethylamino)methyloxazole (HPO) has been synthesized, which performed highly selective and sensitive detection of Zn²⁺ ion with a discriminating enhancement over the other metal ions. The binding constant was calculated as 3.07 × 10³ M^-1 with detection limit of 1.22 × 10^-6 M in aqueous solution (CH₃CN-Tris v/v, 1/1, Tris, 10 mM, pH = 7.4). Moreover, the HPO-Zn²⁺ complex could serve as an excellent tartrate anion (TA). The detection mode maybe due to TA detach Zn²⁺ ion from HPO-Zn²⁺ complex leading to resulting in the release of the free probe HPO. As a result, a logic circuit has also been constructed on the basis of Zn²⁺ and TA as chemical inputs. Furthermore, fluorescence imaging experiments showed that probe HPO could be used as an effective fluorescent probe for detecting Zn²⁺ and TA in living cells.

Boolean-chemotaxis of logibots deciphering the motions of self-propelling microorganisms

We demonstrate the feasibility of a self-propelling mushroom motor, namely a 'logibot', as a functional unit for the construction of a host of optimized binary logic gates. Emulating the chemokinesis of unicellular prokaryotes or eukaryotes, the logibots made stimuli responsive conditional movements at varied speeds towards a pair of acid-alkali triggers. A series of integrative logic operations and cascaded logic circuits, namely, AND, NAND, NOT, OR, NOR, and NIMPLY, have been constructed employing the decisive chemotactic migrations of the logibot in the presence of the pH gradient established by the sole or coupled effects of acid (HCl-catalase) and alkali (NaOH) drips inside a peroxide bath. The imposed acid and/or alkali triggers across the logibots were realized as inputs while the logic gates were functionally reconfigured to several operational modes by varying the pH of the acid-alkali inputs. The self-propelling logibot could rapidly sense the external stimuli, decide, and act on the basis of intensities of the pH triggers. The impulsive responses of the logibots towards and away from the external acid-alkali stimuli were interpreted as the potential outputs of the logic gates. The external stimuli responsive self-propulsion of the logibots following different logic gates and circuits can not only be an eco-friendly alternative to the silicon-based computing operations but also be a promising strategy for the development of intelligent pH-responsive drug delivery devices.

Molecular logic gates: the past, present and future

The field of molecular logic gates originated 25 years ago, when A. P. de Silva published a seminal article in Nature. Stimulated by this ground breaking research, scientists were inspired to join the race to simulate the workings of the fundamental components of integrated circuits using molecules. The rules of this game of mimicry were flexible, and have evolved and morphed over the years. This tutorial review takes a look back on and provides an overview of the birth and growth of the field of molecular logics. Spinning-off from chemosensor research, molecular logic gates quickly proved themselves to be more than intellectual exercises and are now poised for many potential practical applications. The ultimate goal of this vein of research became clearer only recently - to "boldly go where no silicon-based logic gate has gone before" and seek out a new deeper understanding of life inside tissues and cells.

A highly sensitive fluorescent probe for bioimaging zinc ion in living cells and zebrafish models

A simple OFF–ON fluorescent probe was prepared and successfully applied for bioimaging Zn²⁺ in living systems.

Structural characterization of a fluorescein hydrazone molecular switch with application towards logic gates

A new polymorph of fluorescein hydrazone was fully characterized via single X-ray crystallography. In addition, multiple logic circuits and a Half-Adder operator were designed using the fluorescence and UV-Vis switching responses of the fluorescein compound to different metal cations and pH changes.

Fluorescent and cooperative ion pair receptor based on tolan for Na+ (or Li+) and HSO4-: logic AND gate

A tolan derivative was synthesized as a fluorescent and cooperative ion pair receptor. As both Na⁺ and HSO₄^- ions were complexed to the receptor, only substantial fluorescence was quenched. Thus, it also acts as a logic AND gate.

A Two-Input Fluorescent Logic Gate for Glutamate and Zinc

The direct visualization of neurotransmitters is a continuing problem in neuroscience; however, functional fluorescent sensors for organic analytes are still rare. Herein, we describe a fluorescent sensor for glutamate and zinc ions. The sensor acts as a fluorescent logic gate, giving a turn-off response to glutamate or zinc ion alone. The combination of analytes produces a large increase in fluorescence. This type of sensor will aid in the study of neurotransmission, in this case, for neurons that copackage high concentrations of zinc and glutamate.

Proof of principle of a three-input AND–INHIBIT–OR combinatorial logic gate array

A designed molecule provides a fluorescent signal according to a combinatorial logic array comprised of three-input AND, three-input INHIBIT and two-input OR logic gates.

A multi-stimuli responsive switch as a fluorescent molecular analogue of transistors

Although the quantum nature of molecules makes them specially suitable for mimicking the operation of digital electronic elements, molecular compounds can also be envisioned to emulate the behavior of analog devices. In this work we report a novel fluorescent three-state switch capable of reproducing the analog response of transistors, an ubiquitous device in modern electronics. Exploiting the redox and thermal sensitivity of this compound, the amplitude of its fluorescence emission can be continuously modulated, in a similar way as the output current in a transistor is amplified by the gate-to-source voltage.

Turn-On Near-Infrared Fluorescent Sensor for Selectively Imaging Serotonin

A molecular imaging tool that provides for the direct visualization of serotonin would significantly aid in the investigation of neuropsychiatric disorders that are attributed to its neuronal dysregulation. Here, the design, synthesis, and evaluation of NeuroSensor 715 (NS715) is presented. NS715 is the first molecular sensor that exhibits a turn-on near-infrared fluorescence response toward serotonin. Density functional theory calculations facilitated the design of a fluorophore based on a coumarin-3-aldehyde scaffold that derives from an electron-rich 1,2,3,4-tetrahydroquinoxaline framework, which provides appropriate energetics to prevent the hydroxyindole moiety of serotonin from quenching its fluorescence emission. Spectroscopic studies revealed that NS715 produces an 8-fold fluorescence enhancement toward serotonin with an emission maximum at 715 nm. Accompanying binding studies indicated NS715 displays a 19-fold selective affinity for serotonin and a modest affinity for catecholamines over other primary-amine neurotransmitters. The utility of NS715 toward neuroimaging applications was validated by selectively labeling and directly imaging norepinephrine within secretory vesicles using live chromaffin cells, which serve as a model system for specialized neurons that synthesize, package, and release only a single, unique type of neurotransmitter. In addition, NS715 effectively differentiated between cell populations that express distinct neurotransmitter phenotypes.

A rhodamine embedded bio-compatible smart molecule mimicking a combinatorial logic circuit and ‘key-pad lock’ memory device for defending against information risk

A rhodamine-based chemosensor LC with a colorimetric response towards Al³⁺ and Cu²⁺ and only a fluorescence response to Al³⁺ enables us to fabricate a ‘key-pad-logic’ function.

A paper-based lanthanide smart device for acid–base vapour detection, anti-counterfeiting and logic operations

A paper-based lanthanide smart device was designed for naked-eye detection of acid–base vapors with quick response and good reversibility; the applications of this device were also expanded to anti-counterfeiting and logic operations.

White emission magnetic nanoparticles as chemosensors for sensitive colorimetric and ratiometric detection, and degradation of ClO⁻ and SCN⁻ in aqueous solutions based on a logic gate approach

Fluorescent chemosensors for detecting single anions have been largely synthesized. However, the simultaneous detection and degradation of multiple anions remain a major challenge. Herein we report the synthesis of a white emission nanoprobe on the basis of a Coumarin-Rhodamine CR1-Eu complex coordinated to dipicolinic acid (dpa)-PEG-Fe3O4 nanoparticles for the selective detection of ClO(-) and SCN(-) ions on controlling by a logic gate. The obtained nanoprobe exhibits three individual primary colors (blue, green, and red) as well as white emission at different excitation energies. Interestingly, this nanoprobe shows a marked rose red to violet emission color change in response to ClO(-), a reversible violet to rose red emission color change in response to SCN(-), and high ClO(-) and SCN(-) selectivity and sensitivity with a detection limit of 0.037 and 0.250 nM, respectively. Furthermore, the SCN(-) and ClO(-) can degrade simultaneously through the redox reaction between ClO(-) and SCN(-).

Small molecular logic systems can draw the outlines of objects via edge visualization

The recently-discovered ability of small logical molecules to recognize edges is exploited to achieve outline drawing from binary templates. Outlines of arbitrary curvature, several colours and thicknesses down to 1 mm are drawn in around 30 min or less by employing a common laboratory two-colour ultraviolet lamp. The outlines and the light dose-driven XOR logic with fluorescence output or 'off-on-off' action which is observed in the irradiated regions are modelled by combining foundational principles of photochemistry, acid-base neutralization and diffusion.

A coordination and ligand replacement based three-input colorimetric logic gate sensing platform for melamine, mercury ions, and cysteine

A three-input colorimetric logic gate of melamine, cysteine, and Hg²⁺using Au NP has been reported, in which the colour changes of the Au NPs solution provide sensitive and selective detections of melamine, cysteine, and Hg²⁺.

“AND” luminescent “reactive” molecular logic gates: a gateway to multi-analyte bioimaging and biosensing

This feature article focuses on the recent development of “AND” luminescent molecular logic gates, in which the optical output is produced in response to multiple (bio)chemical inputs and through cascades of covalent bond-modifying reactions triggered by target (bio)analytes, for biosensing and bioimaging applications in complex media.