Surfactant modulated aggregation induced enhancement of emission (AIEE)--a simple demonstration to maximize sensor activity

• Published in: Analyst (London) Vol. 141; no. 1; pp. 225 - 235
• Main Authors: Bhowmick, Rahul, Saleh Musha Islam, Abu, Katarkar, Atul, Chaudhuri, Keya, Ali, Mahammad
• Format: Journal Article
• Language: English
• Published: England 07.01.2016
• Subjects: Agglomeration; Charging; Chemistry Techniques, Analytical - instrumentation; Dynamics; Emission; Fluorescence; Fluorescence Polarization; Fluorescent Dyes - chemistry; Hep G2 Cells; Humans; Hydrogen-Ion Concentration; Imaging; Limit of Detection; Mercury - analysis; Mercury - chemistry; Microstructure; Movements; Rhodamines - chemistry; Sodium Dodecyl Sulfate - chemistry; Surface-Active Agents - chemistry
• ISSN: 0003-2654; 1364-5528
• DOI: 10.1039/c5an01916h

A new type of easily synthesized rhodamine-based chemosensor L(3), with potential NO2 donor atoms, selectively and rapidly recognizes Hg(2+) ions in the presence of all biologically relevant metal ions and toxic heavy metals. A very low detection limit (78 nM) along with cytoplasmic cell imaging applications with no or negligible cytotoxicity indicate good potential for in vitro/in vivo cell imaging studies. SEM and TEM studies reveal strongly agglomerated aggregations in the presence of 5 mM SDS which turn into isolated core shell microstructures in the presence of 9 mM SDS. The presence of SDS causes an enhanced quantum yield (φ) and stability constant (Kf) compared to those in the absence of SDS. Again, the FI of the [L(3)-Hg](2+) complex in an aqueous SDS (9 mM) medium is unprecedentedly enhanced (∼143 fold) compared to that in the absence of SDS. All of these observations clearly manifest in the enhanced rigidity of the [L(3)-Hg](2+) species in the micro-heterogeneous environment significantly restricting its dynamic movements. This phenomenon may be ascribed as an aggregation induced emission enhancement (AIEE). The fluorescence anisotropy assumes a maximum at 5 mM SDS due to strong trapping (sandwiching) of the doubly positively charged [L(3)-Hg](2+) complex between two co-facial laminar microstructures of SDS under pre-miceller conditions where there is a strong electrostatic interaction that causes an improved inhibition to dynamic movement of the probe-mercury complex. On increasing the SDS concentration there is a phase transition in the SDS microstructures and micellization starts to prevail at SDS ≥ 7.0 mM. The doubly positively charged [L(3)-Hg](2+) complex is trapped inside the hydrophobic inner core of the micelle which is apparent from the failure to quench the fluorescence of the complex on adding 10 equivalents of H2EDTA(2-) solution but in the absence of SDS it is quenched effectively.