Self-Assembled Near-Infrared Dye Nanoparticles as a Selective Protein Sensor by Activation of a Dormant Fluorophore

Design of selective sensors for a specific analyte in blood serum, which contains a large number of proteins, small molecules, and ions, is important in clinical diagnostics. While metal and polymeric nanoparticle conjugates have been used as sensors, small molecular assemblies have rarely been exploited for the selective sensing of a protein in blood serum. Herein we demonstrate how a nonspecific small molecular fluorescent dye can be empowered to form a selective protein sensor as illustrated with a thiol-sensitive near-IR squaraine (<b>Sq</b>) dye (λ_abs= 670 nm, λ_em= 700 nm). The dye self-assembles to form nonfluorescent nanoparticles (<i>D</i>_h = 200 nm) which selectively respond to human serum albumin (HSA) in the presence of other thiol-containing molecules and proteins by triggering a green fluorescence. This selective response of the dye nanoparticles allowed detection and quantification of HSA in blood serum with a sensitivity limit of 3 nM. Notably, the <b>Sq</b> dye in solution state is nonselective and responds to any thiol-containing proteins and small molecules. The sensing mechanism involves HSA specific controlled disassembly of the <b>Sq</b> nanoparticles to the molecular dye by a noncovalent binding process and its subsequent reaction with the thiol moiety of the protein, triggering the green emission of a dormant fluorophore present in the dye. This study demonstrates the power of a self-assembled small molecular fluorophore for protein sensing and is a simple chemical tool for the clinical diagnosis of blood serum

Exfoliation of Reduced Graphene Oxide with Self-Assembled π‑Gelators for Improved Electrochemical Performance

Among several methodologies to improve the solution processing of graphene-based materials, noncovalent functionalization has been considered as the simplest and nondestructive method. Herein, we show that molecular self-assembly process can be used as a useful tool to exfoliate reduced graphene oxide (RGO), resulting in hybrid materials with improved physical properties. Upon interacting with a π-gelator, the dispersing ability of the RGO increased significantly in most of nonpolar and polar aprotic solvents when compared to the bare one. The amount of RGO dispersed was 1.7–1.8 mg mL^–1 in solvents such as toluene, <i>o</i>-dichlorobenzene (ODCB) and tetrahydrofuran (THF). Morphological studies revealed that aggregation of π-gelator over RGO helps to exfoliate graphene layers to remain as individual sheets with higher surface area. Experimental studies revealed enhanced surface area (250 m² g^–1) and better conductivity (3.7 S m^–1) of the hybrid materials with 30% of RGO content resulting in excellent electrochemical performance (specific capacitance of 181 F g^–1) as electrodes for supercapacitors

Color-Tunable Cyano-Substituted Divinylene Arene Luminogens as Fluorescent π‑Gelators

The synthesis of three cyano-substituted divinylene π-gelators is reported. The modulation of the color is achieved by placing the cyano groups in appropriate position of the conjugated backbone, thus modulating the donor–acceptor interaction. Variable-temperature UV–vis data have been utilized to investigate the self-assembly of the gelators <b>1</b>–<b>3</b> that is governed by a cooperative mechanism. A complete set of photophysical parameters (Φ_F,τ, <i>k</i>_r and <i>k</i>_nr) demonstrate the role of the molecular aggregation in enhanced emission upon self-assembly

Light-Induced Ostwald Ripening of Organic Nanodots to Rods

Ostwald ripening allows the synthesis of 1D nanorods of metal and semiconductor nanoparticles. However, this phenomenon is unsuccessful with organic π-systems due to their spontaneous self-assembly to elongated fibers or tapes. Here we demonstrate the uses of light as a versatile tool to control the ripening of amorphous organic nanodots (ca. 15 nm) of an azobenzene-derived molecular assembly to micrometer-sized supramolecular rods. A surface-confined dipole variation associated with a low-yield (13–14%) <i>trans–cis</i> isomerization of the azobenzene moiety and the consequent dipole–dipole interaction in a nonpolar solvent is believed to be the driving force for the ripening of the nanodots to rods

Synthesis and Properties of Amphiphilic Photoresponsive Gelators for Aromatic Solvents

A sugar-based photoresponsive supergelator, <i>N</i>-glycosylazobenzene that shows selective gelation of aromatic solvents is described. The partial <i>trans–cis</i> isomerization of the azobenzene moiety allows photoinduced chopping of the entangled gel fibers to short fibers, resulting in controlled fiber length and gel–sol transition. The gelator is useful for the selective removal of toxic aromatic solvents from water

Attogram Sensing of Trinitrotoluene with a Self-Assembled Molecular Gelator

Detection of explosives is of utmost importance due to the threat to human security as a result of illegal transport and terrorist activities. Trinitrotoluene (TNT) is a widely used explosive in landmines and military operations that contaminates the environment and groundwater, posing a threat to human health. Achieving the detection of explosives at a sub-femtogram level using a molecular sensor is a challenge. Herein we demonstrate that a fluorescent organogelator exhibits superior detection capability for TNT in the gel form when compared to that in the solution state. The gel when coated on disposable paper strips detects TNT at a record attogram (ag, 10^–18 g) level (∼12 ag/cm²) with a detection limit of 0.23 ppq. This is a simple and low-cost method for the detection of TNT on surfaces or in aqueous solutions in a contact mode, taking advantage of the unique molecular packing of an organogelator and the associated photophysical properties

Fluorescence Imaging Assisted Photodynamic Therapy Using Photosensitizer-Linked Gold Quantum Clusters

Fluorescence imaging assisted photodynamic therapy (PDT) is a viable two-in-one clinical tool for cancer treatment and follow-up. While the surface plasmon effect of gold nanorods and nanoparticles has been effective for cancer therapy, their emission properties when compared to gold nanoclusters are weak for fluorescence imaging guided PDT. In order to address the above issues, we have synthesized a near-infrared-emitting gold quantum cluster capped with lipoic acid (L-AuC with (Au)₁₈(L)₁₄) based nanoplatform with excellent tumor reduction property by incorporating a tumor-targeting agent (folic acid) and a photosensitizer (protoporphyrin IX), for selective PDT. The synthesized quantum cluster based photosensitizer PFL-AuC showed 80% triplet quantum yield when compared to that of the photosensitizer alone (63%). PFL-AuC having 60 μg (0.136 mM) of protoporphyrin IX was sufficient to kill 50% of the tumor cell population. Effective destruction of tumor cells was evident from the histopathology and fluorescence imaging, which confirm the <i>in vivo</i> PDT efficacy of PFL-AuC

Transforming a <i>C</i>₃‑Symmetrical Liquid Crystal to a π‑Gelator by Alkoxy Chain Variation

Rational understanding of the structural features involving different noncovalent interactions is necessary to design a liquid crystal (LC) or an organogelator. Herein, we report the effect of the number and positions of alkoxy chains on the self-assembly induced physical properties of a few π-conjugated molecules. For this purpose, we designed and synthesized three <i>C</i>₃-symmetrical molecules based on oligo­(<i>p</i>-phenylenevinylene), <i><b>C</b></i>_<b>3</b><b>OPV1</b>–<b>3</b>. The self-assembly properties of these molecules are studied in the solid and solution states. All of the three molecules follow the isodesmic self-assembly pathway. Upon cooling from isotropic melt, <i><b>C</b></i>_<b>3</b><b>OPV1</b> having nine alkoxy chains (−OC₁₂H₂₅) formed a columnar phase with two-dimensional rectangular lattice and retained the LC phase even at room temperature. Interestingly, when one of the −OC₁₂H₂₅ groups from each of the end benzene rings is knocked out, the resultant molecule, <i><b>C</b></i>_<b>3</b><b>OPV2</b> lost the LC property, however, transformed as a gelator in toluene and <i>n</i>-decane. Surprisingly, when the −OC₁₂H₂₅ group from the middle position is removed, the resultant molecule <i><b>C</b></i>_<b>3</b><b>OPV3</b> failed to form either the LC or the gel phases

Conjugated Random Donor–Acceptor Copolymers of [1]Benzothieno[3,2‑<i>b</i>]benzothiophene and Diketopyrrolopyrrole Units for High Performance Polymeric Semiconductor Applications

Three-component random copolymers having different ratios of [1]­benzothieno­[3,2-<i>b</i>]­benzothiophene (BTBT) and diketopyrrolopyrrole (DPP) units were synthesized, and their application in organic field effect transistors (OFET) has been discussed. These low band gap polymers exhibit p-type semiconducting properties, and it has been observed that increase in the percentage composition of the fused chalcogenophene (BTBT) in the polymer backbone significantly improves the charge carrier mobility (μ_h) up to 2.47 cm² V^–1 s^–1. The GIXRD technique and AFM have been used to explain the influence of BTBT on the nature of molecular packing in the polymer thin films. These results unveil the role of the effective conjugation length as well as the intermolecular ordering of the polymer chains on the charge carrier transport in OFET

Aligned 1‑D Nanorods of a π‑Gelator Exhibit Molecular Orientation and Excitation Energy Transport Different from Entangled Fiber Networks

Linear π-gelators self-assemble into entangled fibers in which the molecules are arranged perpendicular to the fiber long axis. However, orientation of gelator molecules in a direction parallel to the long axes of the one-dimensional (1-D) structures remains challenging. Herein we demonstrate that, at the air–water interface, an oligo­(<i>p</i>-phenylenevinylene)-derived π-gelator forms aligned nanorods of 340 ± 120 nm length and 34 ± 5 nm width, in which the gelator molecules are reoriented parallel to the long axis of the rods. The orientation change of the molecules results in distinct excited-state properties upon local photoexcitation, as evidenced by near-field scanning optical microscopy. A detailed understanding of the mechanism by which excitation energy migrates through these 1-D molecular assemblies might help in the design of supramolecular structures with improved charge-transport properties