Editorial Feature

Researchers Develop a Novel Opto-Chemical Security Device with Dual-Password Protection

Researchers from India have developed a simple process to fabricate a novel device that utilises the dual ion spectral responsive properties of a commercially available chemosensor molecule- Harmin (HM). The Device contains a dual sensing channel, that unlike other devices of a similar nature, can provide protection for both password and pattern recognition.

There has been a recent surge in research to develop data processing and information protection platforms by using molecules that can mimic the operation of electronic logic gates. There has been a huge effort to produce molecular scale logic devices that can process data whilst providing protection by authorizing password entries. There have been many molecules tested to date and many of devices have come about from it. However, these devices all rely on multiple input channels with only a single output channel.

Many devices so far are only able to read a single password and are only practically operable in a single solvent system. A way to circumnavigate this problem is to provide a functional integration of different mediums in a targeted synthesis process.

Based on this approach, the researchers developed a novel molecular keypad lock with multiple inputs, outputs and dual-channel fluorescence outputs. It also possesses password and pattern recognition abilities, something which has not been produced before for this type of device. The system with the device can respond to altered input keys and authorise different password entries, assembled from the same set of keys.

The researchers used a molecule known as Harmin, which is a commercially available chemosensor molecule. It is fabricated from a tricyclic system that contains two hydrogen bonding sites at the adjacent positions. Within the molecule, an indole and pyridine ring act as the proton donor and acceptor sites, respectively. These two sites form the basis of the dual sensing mechanism by its ability to sense two anions simultaneously.

The device can process the different opto-chemical patterns, as a fluorescence output at specific wavelengths, which provides an additional layer of protection that exploits both password and pattern recognition. The system has the potential to provide highly secured combinational locks at the molecular level, that could be used to provide real-time and on-site applications for user authentication.

After a large testing period, the sensing molecule HM was found to be sensitive, and induced an optical response, to F- and HSO4- ions, suspended in acetonitrile. The F- molecules bind to the pyridine ring and form a hydrogen-bonded complex. The formation quenches the fluorescence at 365 nm, and this acts as the “OFF” switch. The incorporation of HSO4-to the F—-HM complex returns the system to its original fluorescence and acts as the “ON” switch.

To make the device reversible, the researchers employed a third input channel at 415 nm. The third output is considered the difference between the 365 nm and 415 nm channels. The combination of 3 input channels allows the device to have a specific combination of emission states, depending on the combination used. This has allowed this novel system to successfully operate with dual passwords, but with a similar output mode.

The interesting feature of this device is that two passwords can generate the same final optical state, but are distinguishable as they follow different optical trajectories. This is a feature that allows the device to distinguish between correct and incorrect passwords.

The opto-chemical lock itself features a transparent quartz cylindrical flow system, where the acetonitrile solvent flows through continuously. There are four automated piston driven injectors containing solutions of water, HM, F- and HSO4-, attached at different points along the cylinder. The injectors respond by the corresponding input devices, depending on the ON/OFF state, where an authorised user can access the lock. After a pre-set amount of time, if no users are authorised, then the injectors stop and the device becomes inaccessible. The lock concept is made up of a combination of optical and chemical building blocks- an opto-chemical approach.

Conventional chemical password entry implies optical monitoring after full password entry. This device has novelty in its dual channel monitoring processes that governs the whole process elements of multiple password entries. The system also can become locked after accepting wrong entries, at any step. This is only a prototype but the novelty and practical application carry great potential for future optimisation, advancement and commercialization.


Majumdar T., Haldar B., Mallick A., A Strategic Design of an Opto-Chemical Security Device with Resettable and Reconfigurable Password Based Upon Dual Channel Two-in-One Chemosensor Molecule, Scientific Reports, 2017, 7, 42811

Image Credit: Shutterstock.com/MaksimKabakou

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