Collective Effects Influencing Fluorescence Emission

A Mini Review on Surface-Enhanced Raman Scattering based Nanoclusters for Sensing and Imaging Applications

Background:

The invention of enhanced Raman scattering by adsorbing molecules on nanostructured metal surfaces is a milestone in the development of spectroscopic and analytical techniques. Important experimental and theoretical efforts were geared towards understanding the Surface Enhanced Raman Scattering effect (SERS) and evaluating its significance in a wide range of fields in different types of ultrasensitive sensing applications.

Methods:

Metal nanoclusters have been widely studied due to their unique structure and individual properties, which place them among single metal atoms and larger nanoparticles. In general, the nanoparticles with a size less than 2 nm is defined as nanoclusters (NCs) and they possess distinct optical properties. In addition, the excited electrons from absorption bands results in the emission of positive luminescence associated to the quantum size effect in which separate energy levels are produced.

Results:

It is demonstrated that fluorescent based SERS investigations of metal nanoparticles have showed more photostability, high compatibility, and good water solubility, has resulted in high sensitivity, better imaging and sensing experience in the biomedical applications.

Conclusion:

In the present review, we report recent trends in the synthesis of metal nanoclusters and their applications in biosensing and bio-imaging applications due some benefits including cost-effectiveness, easy synthesis routes and less consumption of sample volumes. Outcomes of this study confirms that SERS based fluorescent nanoclusters could be one of thrust research areas in biochemistry and biomedical engineering.

Excitons in Carbonic Nanostructures

Unexpectedly bright photoluminescence emission can be observed in materials incorporating inorganic carbon when their size is reduced from macro–micro to nano. At present, there is no consensus in its understanding, and many suggested explanations are not consistent with the broad range of experimental data. In this Review, I discuss the possible role of collective excitations (excitons) generated by resonance electronic interactions among the chromophore elements within these nanoparticles. The Förster-type resonance energy transfer (FRET) mechanism of energy migration within nanoparticles operates when the composing fluorophores are the localized electronic systems interacting at a distance. Meanwhile, the resonance interactions among closely located fluorophores may lead to delocalization of the excited states over many molecules resulting in Frenkel excitons. The H-aggregate-type quantum coherence originating from strong coupling among the transition dipoles of adjacent chromophores in a co-facial stacking arrangement and exciton transport to emissive traps are the basis of the presented model. It can explain most of the hitherto known experimental observations and must stimulate the progress towards their versatile applications.

A highly sensitive fluorescent probe for detection of hydrazine in gas and solution phases based on the Gabriel mechanism and its bioimaging

A new probe 2-benzo[1,2,5]thiadiazol-4-yl-isoindole-1,3-dione (BTI) based on the Gabriel reaction was developed for hydrazine which shows promising selectivity towards hydrazine over other analytes.

Supramolecular functionalization and concomitant enhancement in properties of Au(25) clusters

We present a versatile approach for tuning the surface functionality of an atomically precise 25 atom gold cluster using specific host-guest interactions between β-cyclodextrin (CD) and the ligand anchored on the cluster. The supramolecular interaction between the Au25 cluster protected by 4-(t-butyl)benzyl mercaptan, labeled Au25SBB18, and CD yielding Au25SBB18∩CDn (n = 1, 2, 3, and 4) has been probed experimentally using various spectroscopic techniques and was further analyzed by density functional theory calculations and molecular modeling. The viability of our method in modifying the properties of differently functionalized Au25 clusters is demonstrated. Besides modifying their optoelectronic properties, the CD moieties present on the cluster surface provide enhanced stability and optical responses which are crucial in view of the potential applications of these systems. Here, the CD molecules act as an umbrella which protects the fragile cluster core from the direct interaction with many destabilizing agents such as metal ions, ligands, and so on. Apart from the inherent biocompatibility of the CD-protected Au clusters, additional capabilities acquired by the supramolecular functionalization make such modified clusters preferred materials for applications, including those in biology.