A molecular 1 : 2 demultiplexer

The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Systems that are intelligent have the ability to sense their surroundings, analyze, and respond accordingly. In nature, many biological systems are considered intelligent (e.g., humans, animals, and cells). For man-made systems, artificial intelligence is achieved by massively sophisticated electronic machines (e.g., computers and robots operated by advanced algorithms). On the other hand, freestanding materials (i.e., not tethered to a power supply) are usually passive and static. Hence, herein, the question is asked: can materials be fabricated so that they are intelligent? One promising approach is to use stimuli-responsive materials; these "smart" materials use the energy supplied by a stimulus available from the surrounding for performing a corresponding action. After decades of research, many interesting stimuli-responsive materials that can sense and perform smart functions have been developed. Classes of functions discussed include practical functions (e.g., targeting and motion), regulatory functions (e.g., self-regulation and amplification), and analytical processing functions (e.g., memory and computing). The pathway toward creating truly intelligent materials can involve incorporating a combination of these different types of functions into a single integrated system by using stimuli-responsive materials as the basic building blocks.

Design of "Click" Fluorescent Labeled 2'-deoxyuridines via C5-[4-(2-Propynyl(methyl)amino)]phenyl Acetylene as a Universal Linker: Synthesis, Photophysical Properties, and Interaction with BSA

Microenvironment-sensitive fluorescent nucleosides present attractive advantages over single-emitting dyes for sensing inter-biomolecular interactions involving DNA. Herein, we report the rational design and synthesis of triazolyl push-pull fluorophore-labeled uridines via the intermediacy of C5-[4-(2-propynyl(methyl)amino)]phenyl acetylene as a universal linker. The synthesized nucleosides showed interesting solvatochromic characteristic and/or intramolecular charge transfer (ICT) features. A few of them also exhibited dual-emitting characteristics evidencing our designing concept. The HOMO-LUMO distribution showed that the emissive states of these nucleosides were characterized with more significant electron redistribution between the C5-[4-(2-propynyl(methyl)amino)]phenyl triazolyl donor moiety and the aromatic chromophores linked to it, leading to modulated emission property. The solvent polarity sensitivity of these nucleosides was also tested. The synthesized triazolyl benzonitrile (10C), naphthyl (10E), and pyrenyl (10G) nucleosides were found to exhibit interesting ICT and dual (LE/ICT) emission properties. The dual-emitting pyrenyl nucleoside maintained a good ratiometric response in the BSA protein microenvironment, enabling the switch-on ratiometric sensing of BSA as the only protein biomolecule. Thus, it is expected that the new fluorescent nucleoside analogues would be useful in designing DNA probes for nucleic acid analysis or studying DNA-protein interactions via a drastic change in fluorescence response due to a change in micropolarity.

An intelligent 1:2 demultiplexer as an intracellular theranostic device based on DNA/Ag cluster-gated nanovehicles

The logic device demultiplexer can convey a single input signal into one of multiple output channels. The choice of the output channel is controlled by a selector. Several molecules and biomolecules have been used to mimic the function of a demultiplexer. However, the practical application of logic devices still remains a big challenge. Herein, we design and construct an intelligent 1:2 demultiplexer as a theranostic device based on azobenzene (azo)-modified and DNA/Ag cluster-gated nanovehicles. The configuration of azo and the conformation of the DNA ensemble can be regulated by light irradiation and pH, respectively. The demultiplexer which uses light as the input and acid as the selector can emit red fluorescence or a release drug under different conditions. Depending on different cells, the intelligent logic device can select the mode of cellular imaging in healthy cells or tumor therapy in tumor cells. The study incorporates the logic gate with the theranostic device, paving the way for tangible applications of logic gates in the future.

Implementation of Arithmetic and Nonarithmetic Functions on a Label-free and DNA-based Platform

A series of complex logic gates were constructed based on graphene oxide and DNA-templated silver nanoclusters to perform both arithmetic and nonarithmetic functions. For the purpose of satisfying the requirements of progressive computational complexity and cost-effectiveness, a label-free and universal platform was developed by integration of various functions, including half adder, half subtractor, multiplexer and demultiplexer. The label-free system avoided laborious modification of biomolecules. The designed DNA-based logic gates can be implemented with readout of near-infrared fluorescence, and exhibit great potential applications in the field of bioimaging as well as disease diagnosis.

A RET-supported logic gate combinatorial library to enable modeling and implementation of intelligent logic functions

A logic gate combinatorial library, including basic logic gates, a single three-input NOR gate, and combinatorial gates to realize intelligent logic functions (keypad-lock, parity checker) is constructed.

Boolean logic gates integrate multiple digital inputs into a digital output. Among these, logic gates based on nucleic acids have attracted a great deal of attention due to the prospect of controlling living systems in the way we control electronic computers. Herein, by employing Thioflavin T (ThT) as a signal transducer, we integrated multiple components based on RET (a type of proto-oncogene) into a logic gate combinatorial library, including basic logic gates (NOR, INHIBIT, IMPLICATION), a single three-input NOR gate, and combinatorial gates (INHIBIT–OR, NOT–AND–NOR). In this library, gates were connected in series where the output of the previous gate was the input for the next gate. Subsequently, by taking advantage of the library, some intelligent logic functions were realized. Expectedly, a biocomputing keypad-lock security system was designed by sequential logic operations. Moreover, a parity checker which can identify even numbers and odd numbers from natural numbers was established successfully. This work helps elucidate the design rules by which simple logic can be harnessed to produce diverse and complex calculations by rewiring communication between different gates. Together, our system may serve as a promising proof of principle that demonstrates increased computational complexity by linking multiple logic gates together.

Fluorescent 1:2 demultiplexer and half-subtractor based on the hydrolysis of N-salicylidene-3-aminopyridine

In moist chloroform solution, the ultraviolet light irradiation would cause N-salicylidene-3-aminopyridine (L) to hydrolyze into salicylaldehyde and 3-aminopyridine. To consider an optical signal (UV light) and a chemical signal (Zn(2+)) as inputs, the luminescence signals as outputs, the logic behavior of compound L was investigated. Interestingly, excited by two different wavelengths lights, two sharp distinct fluorescent spectra were collected. Consequently, a fluorescent 1:2 demultiplexer and a fluorescent half-subtractor were respectively expressed.

Development of a DNA sensor using a molecular logic gate

This communication reports the increase in fluorescence resonance energy transfer (FRET) efficiency between two laser dyes in the presence of deoxyribonucleic acid (DNA). Two types of molecular logic gates have been designed where DNA acts as input signal and fluorescence intensity of different bands are taken as output signal. Use of these logic gates as a DNA sensor has been demonstrated.

Enzyme-based D-flip-flop memory system

The enzyme system was used to mimic the D-flip-flop memory unit. The reversible conversion of NAD(+) and NADH cofactors was used to encode the states of the memory unit, while a mixture of inhibitors was used as the Clock input and the substrates were used as the Data input.

2:1 multiplexing function in a simple molecular system

1-[(Anthracen-9-yl)methylene] thiosemicarbazide shows weak fluorescence due to a photo-induced electron transfer (PET) process from the thiosemicarbazide moiety to the excited anthracene. The anthracene emission can be recovered via protonation of the amine as the protonated aminomethylene as an electron-withdrawing group that suppresses the PET process. Similarly, chelation between the ligand and the metal ions can also suppress the PET process and results in a fluorescence enhancement (CHEF). When solvents are introduced as the third control, a molecular 2:1 multiplexer is constructed to report selectively the inputs. Therefore, a molecular 2:1 multiplexer is realized in a simple molecular system.

OFF-ON-OFF fluorescence switch with T-latch function

A novel molecular system with characteristics of an OFF-ON-OFF fluorescence switch was designed to integrate the function of a T-latch. In detail, a receptor(1)-fluorophore-receptor(2) architecture was adopted to achieve fluorescence switching upon addition of protons.

Ratiometric fluorescent receptors for both Zn2+ and H2PO4(-) ions based on a pyrenyl-linked triazole-modified homooxacalix[3]arene: a potential molecular traffic signal with an R-S latch logic circuit

A ratiometric fluorescent receptor with a C(3) symmetric structure based on a pyrene-linked triazole-modified homooxacalix[3]arene (L) was synthesized and characterized. This system exhibited an interesting ratiometric detection signal output for targeting cations and anions through switching the excimer emission of pyrene from the "on-off" to the "off-on" type in neutral solution. (1)H NMR titration results suggested that the Zn(2+) center of receptor L·Zn(2+) provided an excellent pathway of organizing anion binding groups for optimal host-guest interactions. It is thus believed that this receptor has potential application in sensing, detection, and recognition of both Zn(2+) and H(2)PO(4)(-) ions with different optical signals. In addition, the fluorescence emission changes by the inputs of Zn(2+) and H(2)PO(4)(-) ions can be viewed as a combinational R-S latch logic circuit at the molecular level.

All-photonic multifunctional molecular logic device

Photochromes are photoswitchable, bistable chromophores which, like transistors, can implement binary logic operations. When several photochromes are combined in one molecule, interactions between them such as energy and electron transfer allow design of simple Boolean logic gates and more complex logic devices with all-photonic inputs and outputs. Selective isomerization of individual photochromes can be achieved using light of different wavelengths, and logic outputs can employ absorption and emission properties at different wavelengths, thus allowing a single molecular species to perform several different functions, even simultaneously. Here, we report a molecule consisting of three linked photochromes that can be configured as AND, XOR, INH, half-adder, half-subtractor, multiplexer, demultiplexer, encoder, decoder, keypad lock, and logically reversible transfer gate logic devices, all with a common initial state. The system demonstrates the advantages of light-responsive molecules as multifunctional, reconfigurable nanoscale logic devices that represent an approach to true molecular information processing units.

Photochemical "triode" molecular signal transducer

A molecular "hexad" in which five bis(phenylethynyl)anthracene (BPEA) fluorophores and a dithienylethene photochrome are organized by a central hexaphenylbenzene unit has been prepared. Singlet-singlet energy transfer among the BPEA units occurs on the 0.4 and 60 ps time scales, and when the dithienylethene is in the open form, the BPEA units fluoresce in the 515 nm region with a quantum yield near unity. When the dithienylethene is photoisomerized by UV light to the closed form, which absorbs in the 500-700 nm region, the closed isomer strongly quenches all of the excited singlet states of BPEA via energy transfer, causing the fluorescence quantum yield to drop to near zero. This photochemical behavior permits the hexad to function in a manner analogous to a triode vacuum tube or transistor. When a solution of the hexad is irradiated with steady-state light at 350 nm and with red light (>610 nm) of modulated intensity, the BPEA fluorescence excited by the 350 nm light is modulated accordingly. The fluorescence corresponds to the output of a triode tube or transistor and the modulated red light to the grid signal of the tube or gate voltage of the transistor. Frequency modulation, amplitude modulation, and phase modulation are all observed. The unusual ability to modulate intense, shorter-wavelength fluorescence with longer-wavelength light could be useful for the detection of fluorescence from probe molecules without interference from other emitters in biomolecular or nanotechnological applications.

Enzyme-based multiplexer and demultiplexer

A digital 2-to-1 multiplexer and a 1-to-2 demultiplexer were mimicked by biocatalytic reactions involving concerted operation of several enzymes. Using glucose oxidase (GOx) and laccase (Lac) as the data input signals and variable pH as the addressing signal, ferrocyanide oxidation in the output channel was selectively activated by one from two inputs, thus mimicking the multiplexer operation. A demultiplexer based on the enzyme system composed of GOx, glucose dehydrogenase (GDH) and horseradish peroxidase (HRP) allowed selective activation of different output channels (oxidation of ferrocyanide or reduction of NAD(+)) by the glucose input. The selection of the output channel was controlled by the addressing input of NAD(+). The designed systems represent important novel components of future branched enzyme networks processing biochemical signals for biosensing and bioactuating.

Towards 'Computer-on-a-Particle' Devices: Optoelectronic 1:2 Demultiplexer Based on Nanostructured Cadmium Sulfide

Nanocrystalline sulfur-doped cadmium sulfide (CdS) prepared by microwave synthesis was investigated. Photoelectrochemical and optical characteristics of sulfur-doped CdS exhibit the photoelectrochemical photocurrent switching effect. Depending on the wavelength and applied bias, the anodic and/or cathodic photocurrent was observed. The unusual behaviour of nanocrystalline CdS allowed the construction of a combinatorial logic system from this material.

Digital Operations with Molecules - Advances, Challenges, and Perspectives

This Review gives a short introduction into molecular logic and focusses then on the latest advances in the field. With regard to complex logic circuits and functions, molecular devices for arithmetic processing (adders and subtractors), multiplexers/demultiplexers, and encoders/decoders are discussed. Further on, the concept of memory for data storage and sequential logic is considered together with the latest results on molecular keypad locks. Molecular logic has been often connected to the future aim of molecular computing. However, albeit the herein described approaches constitute a starting point, major challenges like concatenation of gates, solid state devices and compartmentalization, and alternative concepts (reversible logic, multivalued logic) are waiting ahead. These points are included, as well as a view on alternative applications of molecular logic in bio-inspired approaches, combinatorial chemistry, and materials science.

All-optical integrated logic operations based on chemical communication between molecular switches

Molecular logic gates process physical or chemical "inputs" to generate "outputs" based on a set of logical operators. We report the design and operation of a chemical ensemble in solution that behaves as integrated AND, OR, and XNOR gates with optical input and output signals. The ensemble is composed of a reversible merocyanine-type photoacid and a ruthenium polypyridine complex that functions as a pH-controlled three-state luminescent switch. The light-triggered release of protons from the photoacid is used to control the state of the transition-metal complex. Therefore, the two molecular switching devices communicate with one another through the exchange of ionic signals. By means of such a double (optical-chemical-optical) signal-transduction mechanism, inputs of violet light modulate a luminescence output in the red/far-red region of the visible spectrum. Nondestructive reading is guaranteed because the green light used for excitation in the photoluminescence experiments does not affect the state of the gate. The reset is thermally driven and, thus, does not involve the addition of chemicals and accumulation of byproducts. Owing to its reversibility and stability, this molecular device can afford many cycles of digital operation.