A Fluorescent-Switch-Based Computing Platform in Defending Information Risk

Suppression of Undesirable Isomerization and Intermolecular Reactions of Double Bonds by a Linked Rotaxane Structure

For luminescent materials, the isomerization and intermolecular reactions of their double bonds are often undesirable because they cause a reduction in the luminescence properties of the π-system. Herein, we report a new methodology to simultaneously prevent isomerization and intermolecular reactions by utilizing the steric effect of a linked rotaxane structure. The ring units are covalently linked in order to prevent any undesired shuttling effect from occurring during isomerization. In addition, the insulated structure provides robust optical properties by prevention of intermolecular reactions. Bulky linked rotaxane structures on both sides of the N=N and C=C double bonds suppress E/Z isomerization; photoluminescence quantum yield (PLQY) measurements reveal that this results in suppression of PLQY reduction caused by isomerization. Moreover, an improvement in the stability under light irradiation and air atmosphere is demonstrated.

Excitation wavelength as logic operator

Multiple molecular logic gates were harvested on a single synthesized material, (E)-2-(2-hydroxy-3-methoxybenzylideneamino)phenol (MBAP), by combining excitation wavelength dependent multi-channel fluorescence outputs and the same chemical inputs. Interestingly, the effortless switching of logic behavior was achieved by simply tweaking the excitation wavelength and sometimes the emission wavelengths with no alteration of chemical inputs and the main device molecule, MBAP. Additionally, new generation purely optically driven memory units were designed on the same system supporting an almost infinite number of write-erase cycles since inter-conversion of memory states was completely free from chemical interferences and impurity issues. Two-way memory functions ("erase-read-write-read" and "write-read-erase-read") worked simultaneously on the same system and could be accessed by simple optical switching between two excitation and emission wavelengths. Our optically switchable device might outperform traditional multifunctional logic gates and memory devices that generally employ chemical triggers to switch functionality and memory states. These optically switchable multifunctional molecular logic gates and memory systems might drive smart devices in the near future with high energy efficiency, extended life span, structural and functional simplicity, exclusive reversibility and enhanced data storage density.

Three-Input Molecular Keypad Lock Based on a Norbornadiene-Quadricyclane Photoswitch

The photo- and acidochromic properties of a new generation norbornadiene derivative have been harnessed for the realization of a three-input keypad lock, where a specific sequence of inputs induces a unique output. Reversible quadricyclane/norbornadiene photoisomerization is reported, and this rare feature allows the first example of a norbornadiene-based molecular logic system. The function of this system is clearly rationalized in terms of the interconversion scheme and the absorption spectra of the involved species.

Molecules for security measures: from keypad locks to advanced communication protocols

The idea of using molecules in the context of information security has sparked the interest of researchers from many scientific disciplines. This is clearly manifested in the diversity of the molecular platforms and the analytical techniques used for this purpose, some of which we highlight in this Tutorial Review. Moreover, those molecular systems can be used to emulate a broad spectrum of security measures. For a long time, molecular keypad locks enjoyed a clear preference and the review starts off with a description of how these devices developed. In the last few years, however, the field has evolved into something larger. Examples include more complex authentication protocols (multi-factor authentication and one-time passwords), the recognition of erroneous procedures in data transmission (parity devices), as well as steganographic and cryptographic protection.

Sequential logic operations with a molecular keypad lock with four inputs and dual fluorescence outputs

A novel coumarin-rhodamine conjugate was prepared, and its metal binding properties were studied by UV/Vis and fluorescence spectroscopy. The conjugate serves as a ratiometric and highly selective fluorescent sensor for Hg(2+) ions. Its metal-responsive spectral properties were utilized to construct a molecular keypad lock with four inputs and dual fluorescence outputs. The complexity of this molecular logic network can greatly enhance the security level of this device.

Complex logic functions implemented with quantum dot bionanophotonic circuits

We combine quantum dots (QDs) with long-lifetime terbium complexes (Tb), a near-IR Alexa Fluor dye (A647), and self-assembling peptides to demonstrate combinatorial and sequential bionanophotonic logic devices that function by time-gated Förster resonance energy transfer (FRET). Upon excitation, the Tb-QD-A647 FRET-complex produces time-dependent photoluminescent signatures from multi-FRET pathways enabled by the capacitor-like behavior of the Tb. The unique photoluminescent signatures are manipulated by ratiometrically varying dye/Tb inputs and collection time. Fluorescent output is converted into Boolean logic states to create complex arithmetic circuits including the half-adder/half-subtractor, 2:1 multiplexer/1:2 demultiplexer, and a 3-digit, 16-combination keypad lock.

A resettable and reprogrammable DNA-based security system to identify multiple users with hierarchy

Molecular-level security devices have raised ever-increasing interest in recent years to protect data and information from illegal invasion. Prior molecular keypad locks have an output signal dependent upon not only the appropriate combination but also the exact sequence of inputs, but it cannot be reset or reprogrammed. Here, a DNA-based security system with reset and never-reported reprogram function is successfully developed in proof-of-principle, with which one can change the password in case that the system is cracked. The previous password becomes invalid in the reprogrammed security system. Interestingly, more than one password is designed to permit multiple users to access. By harnessing the intrinsic merit of the different passwords, the system can distinguish different user who is endowed with prior authority. The intelligent device is addressed on solid support and facilitates electronic processes, avoiding chemical accumulation in the system by simple removal of the electrode from the input solution and indicating a main avenue for its further development.

DNA-templated Ag nanoclusters as signal transducers for a label-free and resettable keypad lock

We present a unique, label-free and resettable molecular keypad lock that utilizes DNA-modulated Ag nanoclusters (Ag NCs) as signal responsers. The present work demonstrates the first example that exonuclease-catalyzed DNA hydrolysis reaction could be used to achieve the RESET function of a molecular keypad without complicated procedures.

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.

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.

Resettable fluorescence logic gate based on calcein/layered double hydroxide ultrathin films

A fluorescent logic gate was fabricated based on calcein/layered double hydroxide ultrathin films (UTFs) via alternate assembly technique, which exhibits high stability, reversibility, and resettability. The logic gate was manipulated by utilizing pH value, Hg(2+) and Cl(-) ion as inputs, and the fluorescence emission of the (calcein/LDH)(16) UTF as output, serving as a three-input logic gate that combines the YES and INHIBIT operation.

An aptamer-based keypad lock system

An aptamer-based security system mimicking keypad lock function was successfully designed. The system was turned "ON" with a strong fluorescent output signal only when the inputs were added according to the correct combination and exact sequence. Otherwise, the system was kept "OFF" to prevent illegal access.

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.

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.