When a molecule absorbs a photon of appropriate energy, a chain of photophysical events ensues, such as internal conversion or vibrational relaxation (loss of energy in the absence of light emission), fluorescence, intersystem crossing (from singlet state to a triplet state) and phosphorescence, as shown in the Jablonski diagram for organic molecules (Fig. 1). Each of the processes occurs with a certain probability, characterized by decay rate constants (k). It can be shown that the average length of time τ for the set of molecules to decay from one state to another is reciprocally proportional to the rate of decay: τ = 1/k. This average length of time is called the mean lifetime, or simply lifetime. It can also be shown that the lifetime of a photophysical process is the time required by a population of N electronically excited molecules to be reduced by a factor of e. Correspondingly, the fluorescence lifetime is the time required by a population of excited fluorophores to decrease exponentially to N/e via the loss of energy through fluorescence and other non-radiative processes. The lifetime of photophycal processes vary significantly from tens of femotoseconds for internal conversion1,2 to nanoseconds for fluorescence and microseconds or seconds for phosphorescence.1






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Figure 1


Jablonski diagram and a timescale of photophysical processes for organic molecules.

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Fluorescence Lifetime Measurements and Biological Imaging

The field of nanotechnology mainly encompasses with biology, physics, chemistry and material sciences and it develops novel therapeutic nanosized materials for biomedical and pharmaceutical applications. The biological syntheses of nanoparticles are being carried out by different macro-microscopic organisms such as plant, bacteria, fungi, seaweeds and microalgae. The biosynthesized nanomaterials have been effectively controlling the various endemic diseases with less adverse effect. Plant contains abundant natural compounds such as alkaloids, flavonoids, saponins, steroids, tannins and other nutritional compounds. These natural products are derived from various parts of plant such as leaves, stems, roots shoots, flowers, barks, and seeds. Recently, many studies have proved that the plant extracts act as a potential precursor for the synthesis of nanomaterial in non-hazardous ways. Since the plant extract contains various secondary metabolites, it acts as reducing and stabilizing agents for the bioreduction reaction to synthesized novel metallic nanoparticles. The non-biological methods (chemical and physical) are used in the synthesis of nanoparticles, which has a serious hazardous and high toxicity for living organisms. In addition, the biological synthesis of metallic nanoparticles is inexpensive, single step and eco-friendly methods. The plants are used successfully in the synthesis of various greener nanoparticles such as cobalt, copper, silver, gold, palladium, platinum, zinc oxide and magnetite. Also, the plant mediated nanoparticles are potential remedy for various diseases such as malaria, cancer, HIV, hepatitis and other acute diseases.

Biosynthesis of metallic nanoparticles using plant derivatives and their new avenues in pharmacological applications – An updated report

Glucose detection is of great significance in biomedical applications. Principles, methods and recent developments in electrochemical glucose sensors are reviewed here. Special attention is given to the discussion on some problems and bottlenecks in areas of nonenzymatic and enzymatic (glucose oxidase-based) amperometric glucose sensing.

/pdf/recent-advances-in-electrochemical-glucose-biosensors-a-4zf5h9p6ys.pdf

Recent advances in electrochemical glucose biosensors: a review

Nanomedicine Hong Ying Mao,† Sophie Laurent,‡ Wei Chen,*,†,§ Omid Akhavan, Mohammad Imani, Ali Akbar Ashkarran, and Morteza Mahmoudi* †Department of Chemistry, National University of Singapore, 3 Science Drive 3, Singapore 117543, Singapore ‡Department of General, Organic, and Biomedical Chemistry, NMR and Molecular Imaging Laboratory, University of Mons, Avenue Maistriau, 19, B-7000 Mons, Belgium Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542, Singapore Department of Physics, Sharif University of Technology, P.O. Box 11155-9161, Tehran, Iran Institute for Nanoscience and Nanotechnology, Sharif University of Technology, P.O. Box 14588-89694, Tehran, Iran Novel Drug Delivery Systems Department, Iran Polymer and Petrochemical Institute, Tehran, Iran Department of Physics, Faculty of Basic Sciences, University of Mazandaran, Babolsar, Iran Nanotechnology Research Center, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran Department of Nanotechnology, Faculty of Pharmacy, Tehran University of Medical Sciences, Tehran, Iran

Graphene: Promises, Facts, Opportunities, and Challenges in Nanomedicine

This review highlights recent advances towards non-invasive and continuous glucose monitoring devices, with a particular focus placed on monitoring glucose concentrations in alternative physiological fluids to blood.

Glucose Sensing for Diabetes Monitoring: Recent Developments.

Nanomedicine involves measurement and therapy at the level of 1-100 nm. Although the science is still in its infancy, it has major potential applications in diabetes. These include solving needs such as non-invasive glucose monitoring using implanted nanosensors, with key techniques being fluorescence resonance energy transfer (FRET) and fluorescence lifetime sensing, as well as new nano-encapsulation technologies for sensors such as layer-by-layer (LBL) films. The latter might also achieve better insulin delivery in diabetes by both improved islet encapsulation and oral insulin formulations. An 'artificial nanopancreas' could be an alternative closed-loop insulin delivery system. Other applications of nanomedicine include targeted molecular imaging in vivo (e.g. tissue complications) using quantum dots (QDs) or gold nanoparticles, and single-molecule detection for the study of molecular diversity in diabetes pathology.

Nanomedicine and its potential in diabetes research and practice

Alternative, non-electrochemistry-based technologies for continuous glucose monitoring are needed for eventual use in diabetes mellitus. As part of a programme investigating fluorescent glucose sensors, we have developed fibre-optic biosensors using glucose/galactose binding protein (GBP) labelled with the environmentally sensitive fluorophore, Badan. GBP–Badan was attached via an oligohistidine-tag to the surface of Ni–nitrilotriacetic acid (NTA)-functionalized agarose or polystyrene beads. Fluorescence lifetime increased in response to glucose, observed by fluorescence lifetime imaging microscopy of the GBP–Badan-beads. Either GBP–Badan agarose or polystyrene beads were loaded into a porous chamber at the end of a multimode optical fibre. Fluorescence lifetime responses were recorded using pulsed laser excitation, high speed photodiode detection and time-correlated single-photon counting. The maximal response was at 100 mM glucose with an apparent Kd of 13 mM (agarose) and 20 mM (polystyrene), and good working-day stability was demonstrated. We conclude that fluorescence lifetime fibre-optic glucose sensors based on GBP–Badan are suitable for development as clinical glucose monitors.

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A fluorescence lifetime-based fibre-optic glucose sensor using glucose/ galactose-binding protein

Fluorescence lifetime spectroscopy and imaging of nano-engineered glucose sensor microcapsules based on glucose/galactose-binding protein.

Fluorescence-based sensing of glucose using engineered glucose/galactose-binding protein: a comparison of fluorescence resonance energy transfer and environmentally sensitive dye labelling strategies.

Faaizah Khan

Papers

Nanomedicine and its potential in diabetes research and practice

A fluorescence lifetime-based fibre-optic glucose sensor using glucose/ galactose-binding protein

Fluorescence lifetime spectroscopy and imaging of nano-engineered glucose sensor microcapsules based on glucose/galactose-binding protein.

Fluorescence-based sensing of glucose using engineered glucose/galactose-binding protein: a comparison of fluorescence resonance energy transfer and environmentally sensitive dye labelling strategies.

Fluorescence intensity- and lifetime-based glucose sensing using an engineered high-Kd mutant of glucose/galactose-binding protein.