Reusable, Ultrasensitive, Patterned Conjugated Polyelectrolyte-Surfactant Complex Film with a Wide Detection Range for Copper Ion Detection

Conjugated polyelectrolytes (CPEs) are emerging as promising materials in the sensor field because they enable high-sensitivity detection of various substances in aqueous media. However, most CPE-based sensors have serious problems in real-world application because the sensor system is operated only when the CPE is dissolved in aqueous media. Here, the fabrication and performance of a water-swellable (WS) CPE-based sensor driven in the solid state are demonstrated. The WS CPE films are prepared by immersing a water-soluble CPE film in cationic surfactants of different alkyl chain lengths in a chloroform solution. The prepared film exhibits rapid, limited water swellability despite the absence of chemical crosslinking. The water swellability of the film enables the highly sensitive and selective detection of Cu²⁺ in water. The fluorescence quenching constant and the detection limit of the film are 7.24 × 10⁶ L mol^-1 and 4.38 nM (0.278 ppb), respectively. Moreover, the film is reusable via a facile treatment. Furthermore, various fluorescent patterns introduced by different surfactants are successfully fabricated by a simple stamping method. By integrating the patterns, Cu²⁺ detection in a wide concentration range (nM-mM) can be achieved.

Copolymers of 4-Trimethylsilyl Diphenyl Acetylene and 1-Trimethylsilyl-1-Propyne: Polymer Synthesis and Luminescent Property Adjustment

Poly(4-trimethylsilyl diphenyl acetylene) (PTMSDPA) has strong fluorescence emission, but its application is limited by the effect of aggregation-caused quenching (ACQ). Copolymerization is a commonly used method to adjust the properties of polymers. Through the copolymerization of 4-trimethylsilyl diphenyl acetylene and 1-trimethylsilyl-1-propyne (TMSP), we successfully realized the conversion of PTMSDPA from ACQ to aggregation-induced emission (AIE) and aggregation-induced emission enhancement (AEE). By controlling the monomer feeding ratio and with the increase of the content of TMSDPA inserted into the copolymer, the emission peak was red-shifted, and a series of copolymers of poly(TMSDPA-co-TMSP) that emit blue-purple to orange-red light was obtained, and the feasibility of the application in explosive detection was verified. With picric acid (PA) as a model explosive, a super-quenching process has been observed, and the quenching constant (K_SV) calculated from the Stern-Volmer equation is 24,000 M^-1, which means that the polymer is potentially used for explosive detection.

Anionic Polyelectrolyte-Induced Aggregation of Basic Orange 21: A Clue toward Metachromasia

The change in the color of chromophore upon being embedded in a biological tissue is known as metachromasia. Basic Orange 21 (BO21) is a cationic polymethine dye that has been implied as a supravital dye, which produces metachromasia in leukocytes. An improved differential counting of leukocytes has been achieved in the clinical setup based on characteristic metachromatic expressions of BO21 for different types of leukocytes. Although BO21 has been utilized as a chromatic indicator for leukocyte counting, there are limited number of investigations that focus on the factors that may be responsible for the spectral shift in absorption and emission spectra of BO21, which leads to its metachromatic behavior. In this work, we have investigated the effect of a synthetic anionic polyelectrolyte, polystyrene sulfonate (PSS), on the photophysical properties of BO21, using steady-state emission, ground-state absorption, and time-resolved emission measurements, to get an understanding of the factors that may be responsible for the spectral shift of BO21 in the cellular environment. PSS induces aggregation of BO21 molecules with large changes in its photophysical properties; this appears to be most likely the mechanism of spectral shift for BO21 reported in the cellular environment. The employment of external stimulus reveals BO21 aggregates to be significantly responsive toward external stimuli, for example, temperature and presence of salt in the medium, which further strengthens the proposal of aggregate formation. Further, we have also employed fluorescence upconversion spectroscopy with subpicosecond time resolution to estimate the excited-state lifetime of BO21.

Rapid aptasensor capable of simply detect tumor markers based on conjugated polyelectrolytes

In this paper, a very simple, easily-operated and universal platform is proposed for tumor marker detection. In this strategy, tumor marker-specific aptamer, which can quench the fluorescence of polyfluorene-based cationic conjugated polyelectrolytes (PFN⁺), are used as recognizing probes. Upon addition of tumor marker, the aptamer can be assembled into the tumor marker-aptamer complex, resulting in fluorescence recovery of PFN⁺ and the detection of the targets. The most widely-used tumor markers, carcinoembryonic antigen (CEA) and fetoprotein (AFP) have been chosen as the model analytes for this work. The sensing method is capable of rapidly detect target protein within 5 min without complex handling procedure and expensive instruments. Compared with previous studies, the assay presented here is really simple and avoids either conjugated polyelectrolytes (CPEs) modification or oligonucleotide labeling. This method also shows a wide detection range of 3 orders of magnitude and the detection limit is 0.316 ng/mL for CEA and 1.76 ng/mL for AFP. Furthermore, the approach requires only a convenient"mix-and-detect" procedure and offers a universal platform for the sensitive detection of any target molecule of choice according to the selected aptamer.

Novel intramolecular π-π-interaction in a BODIPY system by oxidation of a single selenium center: geometrical stamping and spectroscopic and spectrometric distinctions

A new BODIPY system displaying an intramolecular π-π-interaction was synthesized and studied. When the selenium center was oxidized, the substituted phenyl group undergoes π-π stacking with one side of the BODIPY core. The oxidized form showed, not only a down-field shift in the NMR peak, but also splitting due to geometrical changes that arise when going from C_s to C₁. The compound was characterized by X-ray diffraction; DFT methods helped elucidate the influence of the unexpected π-π stack and its connection to the photophysical properties imparted by the Se oxidation.

Visualization of Sweat Fingerprints on Various Surfaces Using a Conjugated Polyelectrolyte

A conformation-variable conjugated polyelectrolyte responding to oppositely charged biomolecules was examined as an imaging agent for the detection of latent fingerprints (LFPs). Sulfonated poly(diphenylacetylene) (SPDPA) produces high-resolution fluorescence (FL) LFP images by simple wetting of the target objects with the polymer solution without any additional treatment. SPDPA readily interacts with LFP sweat components (especially amino acids) via electrostatic interactions, leading to significantly enhanced FL images in a "turn-on" mode. The FL emission enhancement was examined in a model reaction between SPDPA and an amino acid standard. Visualization with SPDPA is effective on various surfaces, including both rough (paper) and smooth (glass and plastic) ones. Moreover, SPDPA readily interacts with extremely thin sweat LFPs, especially on smooth glass surfaces.

Different amine-functionalized poly(diphenylsubstituted acetylenes) from the same precursor

A facile and efficient synthetic route to different amine functionalized poly(diphenyl-substituted acetylenes) from the same precursor polymer is reported. The derived polymers demonstrated versatile applications.

Fluorescence Response of Conjugated Polyelectrolyte in an Immiscible Two-Phase System via Nonelectrostatic Interaction with Surfactants

This paper reports a unique fluorescence (FL) response and diverse applications of conjugated polyelectrolyte (CPE) through nonelectrostatic interaction with appropriate (bio)surfactants in an immiscible two-phase system. A sulfonated microporous conjugated polymer (SMCP) with a conformation-variable intramolecular stacked structure was used as the CPE film. Despite the extremely high hydrophilicity, the SMCP film responded significantly to the hydrophobic circumstances, either physicochemically or electronically, in the presence of water-in-oil (w/o)-type nonionic surfactants with appropriate hydrophile-lipophile balance (HLB) values. The polymer film became fully wet with hydrophobic solvents due to the addition of small amounts of (bio)surfactant to reveal remarkable FL emission enhancement and chromism. Microcontact and inkjet printing using the SMCP film (or SMCP-adsorbed paper) and the surfactant solution as substrate and ink, respectively, provided high-resolution FL images due to the distinctive surfactant-induced FL change (SIFC) characteristic. Moreover, the additional electrostatic interaction of SMCP film with oppositely charged surfactants further enhanced the FL emission. Our findings will help comprehensive understanding of the nonelectrostatic SIFC mechanism of CPEs and development of novel SIFC-active materials.

Assembly of luminescent ordered multilayer thin-films based on oppositely-charged MMT and magnetic NiFe-LDHs nanosheets with ultra-long lifetimes

In this present report, luminescent ordered multilayer thin films (OMFs) based on oppositely-charged inorganic nanosheets and the different oppositely-charged chromophores were fabricated via layer-by-layer assembly method. Exfoliated layered double hydroxides (LDHs) and montmorillonite (MMT) nanosheets with opposite charges can be expected to provide a pseudo electronic microenvironment (PEM) which has not been declared in previous literatures, and transition metal-bearing LDHs nanosheets can offer an additional ferromagnetic effect (FME) for the chromophores at the same time. Surprisingly, the luminescent lifetimes of those OMFs with PEM and FME are significantly prolonged compared with that of the pristine chromophores, even much longer than those of OMFs without oppositely-charged and ferromagnetic architecture. Therefore, it is highly expected that the PEM and FME formed by oppositely-charged and transition metal-bearing inorganic nanosheets have remarkable influence on obtaining better optical property, which suggests a new potential way to manipulate, control and develop the novel light-emitting materials and optical devices.