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A Prasanna de Silva

Publications and source records attributed to A Prasanna de Silva.

10 recordsLinked to original sources
PubMed2006

Molecular computational elements encode large populations of small objects.

Since the introduction of molecular computation, experimental molecular computational elements have grown to encompass small-scale integration, arithmetic and games, among others. However, the need for a practical application has been pressing. Here we present molecular computational identification (MCID), a demonstration that molecular logic and computation can be applied to a widely relevant issue. Examples of populations that need encoding in the microscopic world are cells in diagnostics or beads in combinatorial chemistry (tags). Taking advantage of the small size (about 1 nm) and large 'on/off' output ratios of molecular logic gates and using the great variety of logic types, input chemical combinations, switching thresholds and even gate arrays in addition to colours, we produce unique identifiers for members of populations of small polymer beads (about 100 microm) used for synthesis of combinatorial libraries. Many millions of distinguishable tags become available. This method should be extensible to far smaller objects, with the only requirement being a 'wash and watch' protocol. Our focus on converting molecular science into technology concerning analog sensors, turns to digital logic devices in the present work.

Journal Article↗
PubMed2006

Communicating chemical congregation: a molecular AND logic gate with three chemical inputs as a "lab-on-a-molecule" prototype.

We demonstrate the first three-input molecular AND logic gate based on three chemical inputs as a direct way of detecting congregations of chemical species. The AND gate operates in water and responds to Na+, H+, and Zn2+ inputs with an enhanced fluorescence signal when pre-set concentration thresholds are exceeded. Future "lab-on-a-molecule" devices could have application in medicine for rapid disease screening.

Journal Article↗
PubMed2005

Membrane media create small nanospaces for molecular computation.

Molecular computation is fashionable because of the small device sizes that should be possible. For instance, information processing in nanospaces is widespread in biology. However, experimental cases with computing molecules occupy rather large volumes until now (ca. 1012 nm3). Now we demonstrate small-scale computation using a designed logic gate in spheres of 3 nm radius (volume = ca. 102 nm3) which are produced by detergent micelles. The logic gate accommodated in the small nanospace fluoresces only when both H+ and Na+ ions are available.

Computer Simulation↗
PubMed2005

The Anthracen-9-ylmethyloxy unit: an underperforming motif within the fluorescent PET (photoinduced electron transfer) sensing framework.

Compound, which was designed to act as a fluorescent sensor for calcium according to the PET (Photoinduced Electron Transfer) principle, shows a relatively small Ca2+-induced fluorescence enhancement factor (FE) of 1.8 whereas its close relative is known to display a far higher FE value of 16. Though designed as fluorescent PET sensors for solvent polarity, compounds and also show negligible fluorescence enhancement as their environments are made progressively less polar even though their relatives and show limiting FE values of 53 and 3, respectively. Indeed, and are useful since they are fluorescent sensors for solvent polarity without being affected by Bronsted acidity. The poor sensory performance of and relative to their cousins is attributed to the presence of an oxygen proximal to the 9-position of an anthracene unit, which opens up a CT (charge transfer) channel. Normal PET sensing service is resumed when the offending oxygen is deleted.

Journal Article↗
PubMed2004

Modulation of the sensitive temperature range of fluorescent molecular thermometers based on thermoresponsive polymers.

Fluorescent molecular thermometers based on polymers showing a temperature-induced phase transition and labeled with polarity-sensitive fluorescent benzofurazans are the most sensitive known. Here we show a simple and effective method for modulating the sensitive temperature ranges of fluorescent molecular thermometers based on such temperature-responsive polymers. 4-N-(2-acryloyloxyethyl)-N-methylamino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole was adopted as a polarity-sensitive fluorescent benzofurazan, and nine copolymers of two kinds of acrylamide derivative (N-n-propylacrylamide, N-isopropylacrylamide, and/or N-isopropylmethacrylamide) with a small amount of DBD-AE were obtained. The fluorescence intensities of these copolymers in aqueous solution sharply increased with increasing temperature over a small range (6-7 degrees C). In contrast, these fluorescent molecular thermometers differed from one another in the sensitive temperature range (between 20 and 49 degrees C). Moreover, the sensitive temperature ranges were well related to the acrylamide ratios in feed. In addition, the responses from these fluorescent molecular thermometers to the change in temperature were reversible and exactly repeatable during 10 cycles of heating and cooling (relative standard deviation of the fluorescence intensity, 0.44-1.0%).

Benzoxazoles↗
PubMed2004

Molecular-scale logic gates.

Currently available approaches to molecular-scale logic gates are summarized and compared. These include: chemically-controlled fluorescent and transmittance-based switches concerned with small molecules, DNA oligonucleotides with fluorescence readout, oligonucleotide reactions with DNA-based catalysts, chemically-gated photochromics, reversibly denaturable proteins, molecular machines with optical and electronic signals, two-photon fluorophores and multichromophoric transient optical switches. The photochemical principles of electron and energy transfer are involved in several of these approaches. More complex molecular logic systems with reconfigurability and superposability provide contrasts with current semiconductor electronics. Integration of simple logic functions to produce more complex ones is also discussed in terms of recent developments.

Base Sequence↗
PubMed2003

Fluorescent molecular thermometers based on polymers showing temperature-induced phase transitions and labeled with polarity-responsive benzofurazans.

Poly(N-isopropylacrylamide) in aqueous solution undergoes a phase transition at approximately 32 degrees C. The fluorescence properties of benzofurazans are affected by solvent polarity. We combine these two characteristics for the first time to develop sensitive fluorescent molecular thermometers. Five fluorescent monomers having a benzofurazan skeleton were synthesized, and the copolymers of N-isopropylacrylamide (NIPAM) and a small quantity of the fluorescent monomer were obtained to investigate their fluorescence properties. With increase in temperature, the copolymers in water showed the temperature-induced phase transition at approximately 32 degrees C and the fluorescence intensities of the copolymers concurrently increased. Especially, for the copolymer of 4-N-(2-acryloyloxyethyl)-N-methylamino-7-N,N-dimethylaminosulfonyl-2,1,3-benzoxadiazole and NIPAM, the fluorescence intensity at 37 degrees C was 13.3-fold that seen at 29 degrees C. The sensitive range of temperature of these fluorescent molecular thermometers is changed by the replacement of the NIPAM units by N-isopropylmethacrylamide or N-n-propylacrylamide units in the copolymers. The basis of these fluorescent molecular thermometers is the decrease in the microenvironmental polarities near the main chains of the copolymers with increasing temperature, as confirmed from the maximum emission wavelengths of the benzofurazan units in the copolymers. The responses from the copolymers to the change in temperature are reversible and exactly repeatable during at least 10 cycles of heating and cooling.

Journal Article↗
PubMed2002

Simultaneously multiply-configurable or superposed molecular logic systems composed of ICT (internal charge transfer) chromophores and fluorophores integrated with one- or two-ion receptors.

Integrated "ICT chromophore-receptor" systems show ion-induced shifts in their electronic absorption spectra. The wavelength of observation can be used to reversibly configure the system to any of the four logic operations permissible with a single input (YES, NOT, PASS 1, PASS 0), under conditions of ion input and transmittance output. We demonstrate these with dyes integrated into Tsien's calcium receptor, 1-2. Applying multiple ion inputs to 1-2 also allows us to perform two- or three-input OR or NOR operations. The weak fluorescence output of 1 also shows YES or NOT logic depending on how it is configured by excitation and emission wavelengths. Integrated "receptor(1)-ICT chromophore-receptor(2)" systems 3-5 selectively target two ions into the receptor terminals. The ion-induced transmittance output of 3-5 can also be configured via wavelength to illustrate several logic types including, most importantly, XOR. The opposite effects of the two ions on the energy of the chromophore excited state is responsible for this behaviour. INHIBIT and REVERSE IMPLICATION are two of the other logic types seen here. Integration of XOR logic with a preceding OR operation can be arranged by using three ion inputs. The fluorescence output of these systems can be configured via wavelength to display INHIBIT or NOR logic under two-input conditions. The superposition or multiplicity of logic gate configurations is an unusual consequence of the ability to simultaneously observe multiple wavelengths.

Journal Article↗