Nanomolar Cu²⁺Detection in Water Based on Disassembly of AIEgen: Applications in Blood Serum, Cell Imaging and Complex Logic Circuits

Abstract

Here in, we report self‐assembled aggregates of AIEgen 1, which exhibits excited state intramolecular proton transfer (ESIPT) coupled aggregation induced emission (AIE) with intense green fluorescence (λem=526 nm) in aqueous solution as well as in solid state. AIEgen 1 behaves as disassembly based fluorescent probe for selective and sensitive detection of Cu2+ in drinking water with lowest limit of detection of 0.261 ppb (4.13 nM) (much lower than recommended by EPA). AIEgen 1 finds applications for the detection of Cu2+ in blood serum, environmental (tap, pond and industrial waste water) samples. Probably the interaction of Cu2+ ions at Schiff‐base unit of AIEgen 1 via metal chelation disrupts the self‐assembled aggregates and results in disassembly of the nanorods into smaller spherical nanostructures as also evidenced in DLS, SEM and TEM studies. Incubation of HeLa cells with AIEgen 1 results in fluorescence ‘switch‐on’ showing cell internalization of AIEgen 1 with low cytotoxicity and thus establishes the potential of AIEgen 1 in cell imaging. The reversibility influorescence / absorbance of 1‐Cu2+ complex with EDTA helps in elaboration of various reconfigurable and superposed logic gates such as NOT (at F425, A380), INH (at A430), IMP1 (at A380) and IMP2 (at F526). By observing the output switching in absorbance and fluorescence channels on addition of Cu2+ (In1) and EDTA (In2) as inputs, ‘set‐ reset’ flip flop memory element and complementary IMP/INH logic circuits have been elaborated.

ESIPT‐based AIE luminogens: Design strategies, applications, and mechanisms

“…[ 40 ] The addition of Cu 2+ will induce a remarkable fluorescence quenching, whereas the other metal ions do not interfere with the binding of compound 4 to Cu 2+ (see Figure 4C). [ 40 ] The fluorescence quenching by Cu 2+ has also been observed for other ESIPT‐based AIEgens [ 29, 34, 35, 37, 41, 44, 47, 48, 50, 52, 54, 56 ] and may result from ligand‐to‐metal charge transfer, as has been demonstrated by density functional theory calculations. [ 50 ] The computed highest occupied molecular orbital and lowest unoccupied molecular orbital of a ligand–Cu 2+ complex are localized on ligand and metal center, respectively.…”

“…Therefore, almost all the reported ESIPT‐based AIEgens for detection of metal cations involve SSB or SAA scaffolds, or at least, involve Schiff base or azine bearing an intramolecular hydrogen bond O─H···N. [ 28–57 ]…”

“…By changing the substitutes on the benzene ring and the end of the Schiff base, various SSB derivatives have been developed as ESIPT-based AIEgens. [29,30,32,38,43,44,58,62,116,129,130,[159][160][161][162][163][164][165][166][167][168] The introduction of the strong electron-withdrawing groups into SSB, such as ─F and ─NO 2 , may lead to a red-shift of the emission due to the separation of the electron cloud and an increase of the fluorescence quantum yield. [30] A similar effect can also be achieved by attaching an electron-donor diethylamine group and an electron-acceptor maleonitrile group at different sides of SSB.…”

“…The development of ESIPT‐based AIEgens has attracted great attention in the fields of physics, chemistry, and biology science. A growing number of ESIPT‐based AIEgens have been developed and applied in the detection of cations, [ 28–57 ] anions, [ 34, 35, 41, 43, 58–68 ] and small molecules, [ 69–76 ] bioimaging in the living cell and in vivo, [ 77–116 ] drug delivery systems (DDS), [ 44, 117–119 ] liquid crystal, [ 120–122 ] white light emitters, [ 123–127 ] and latent fingerprinting. [ 56, 128–131 ]…”

Fluorescent Schiff base sensors as a versatile tool for metal ion detection: strategies, mechanistic insights, and applications

“…3A and Table 2). 73 On excitation at 390 nm, the fluorescence spectrum of probe 2 displayed green emission at 526 nm, attributed to the AIE + ESIPT process. Upon gradual addition of an increasing concentration of Cu 2+ , the emission spectrum of probe 2 revealed quenching of emission intensity and saturation was achieved after the addition of 1 mM Cu 2+ .…”