Carbon Quantum Dots–Europium(III) Energy Transfer Architecture Embedded in Electrospun Nanofibrous Membranes for Fingerprint Security and Document Counterspy

Gelatinous lanthanide coordination polymer with aggregation-enhanced antenna effect for ratiometric detection of endogenous alkaline phosphatase

Aggregation-induced emission (AIE) and antenna effect (AE) are two significant behaviors that have attracted increasing attention. However, it is challenging to achieve the synergistic effect of AIE and AE in luminescent materials for more extensive applications. Here, four gelatinous Ln³⁺ coordination polymers (Ln-CPs) are synthesized by self-assembly of ciprofloxacin (CIP), adenosine monophosphate (AMP), and Ln³⁺ ions in aqueous medium. Encouragingly, a remarkable increase in the characteristic fluorescence of Ln³⁺ and a significant decrease in CIP are observed along with increasing concentration of Ln-CPs, which is attributed to the large aggregates formed by self-assembly that strictly constrain the intramolecular motions of antenna ligands, thereby achieving the aggregation-enhanced AE. More meaningfully, Eu-CP not only shows a rice-like morphology at high aggregation state, but also provides an opportunity for the selective detection of alkaline phosphatase (ALP). A new flower-like polymer is formed upon incubating Eu-CP with ALP, accompanied by the fluorescence quenching of Eu³⁺ and recovery of CIP, a ratiometric determination of ALP in the range of 0.1-6.0 U·L^-1 is thus achieved. Additionally, ALP assay in human serum and bioimaging in living cells have been successfully performed. This research opens a new horizon for the fabrication of Ln³⁺-based luminescent materials with promising applications.

Recent Progress in Visualization and Analysis of Fingerprint Level 3 Features

Fingerprints provide sufficient and reliable discriminative characteristics which have been considered one of the most robust evidence for individualization. The limitation of current minutiae-based fingerprint technology seems to be solved with the development of level 3 features since they can offer additional information for problematic fingerprint recognition and even donor profiling. So far, tremendous efforts have been devoted to detecting and analysing the third-level details. This review summarizes the advances in level 3 details with an emphasis on their reliability assessment, visualization methods based on physical interaction, residue-response, mass spectrometry and electrochemical techniques, as well as the potentiality for individualization, donor profiling and even other application scenarios. In the end, we also give a personal perspective on the future direction and the remaining challenges in the third-level-detail-related field. We believe that the new exciting progress is expected in the development of level 3 detail detection and analysis with continued interest and attention to this field.

Heavy metal ion detection using green precursor derived carbon dots

The discovery of carbon dots (CDs) for environmental remediation has gained awareness because of the diverse economically viable and environmental friendly green precursors generated from biowastes and biomass compared to the toxic inorganic quantum dots and CDs prepared from chemical precursors. This review presents the recent progress in green CDs, including their synthesis methods and sensing applications for the detection of heavy metal ions such as Iron (III), Mercury (II), Copper (II), Chromium (VI), Lead (II), Arsenic (III), Cobalt (II), Aluminum (III), Silver (I), and Gold (III) which are prominent environmental pollutants. The comparison based on selectivity, sensitivity, quantum yield, detection limit, linear concentration range, and sensing mechanisms are also reported. This review also covers the performance of doped green CDs using heteroatoms, toward the detection of heavy metal ions. Apart from the future perspectives, this review provides a general guide to use such environmental friendly CDs to detect harmful pollutants.

A Fluorescent Nanosensor for Silver (Ag+) and Mercury (Hg2+) Ions Using Eu (III)-Doped Carbon Dots

Carbon dots doped with Eu³⁺ ions (Eu-Cdots) were prepared by a hydrothermal treatment, using citric acid and urea as precursors and Eu (NO₃)₃ as a europium source. The Eu³⁺ ions are strongly coordinated with the carboxylate groups at the surface of the Cdots and incorporated within the nanographene network in the carbon core. Vibrational spectroscopy provides evidence of such interaction with identification of bands assigned to the stretching of the Eu-O bond. Eu³⁺ doped Cdots have larger diameters then undoped Cdots, but they are divided into smaller domains of sp² carbon. The UV-vis excitation spectrum provides evidence of energy transfer from the Cdots to the Eu³⁺. The luminescence spectrum shows the characteristic sharp peaks of Eu³⁺ in the red part of the visible spectrum and a broad emission of Cdots centered at 450 nm. The luminescence of the Cdots is strongly quenched by Hg²⁺ and Ag⁺, but not by other cations. The quenching mechanism differs significantly depending on the nature of the ion. Both the blue emission of Cdots and the red emission of Eu³⁺ are quenched in the presence of Hg²⁺ while only the emission of the Cdots is affected by the presence of Ag⁺. A ratiometric sensor can be built using the ratio of luminescence intensities of the Cdots to the Eu³⁺ peaks.

Aggregation-Enhanced Energy Transfer for Mitochondria-Targeted ATP Ratiometric Imaging in Living Cells

Förster resonance energy transfer (FRET) from fluorescent nanoparticles to fluorescent dyes is an attractive approach for bioanalysis in living cells. However, the luminescence of the nanoparticle donor/acceptor has not been effectively used to produce highly efficient FRET because the distance between the energy donor and energy acceptor is often larger than the effective FRET radius (about 10 nm) and the uncontrolled rotational and translational diffusion of luminophores. Here, we develop an aggregation-enhanced energy transfer strategy that can overcome the impedance for effective energy transfer. The functional nanoprobes, named TPP-CDs-FITC, are carbon dots (CDs) functionalized with triphenylphosphine (TPP) and ∼117 fluorescein 5-isothiocyanate (FITC) on the surface. In dispersed solution, the 3.8 nm TPP-CDs-FITC show weak FRET efficiency (15.4%). After TPP-instructed mitochondrial targeting, enhanced FRET efficiency (53.2%) is induced due to the aggregation of TPP-CDs-FITC selectively triggered by adenosine triphosphate (ATP) in the mitochondria. The enhanced FRET efficiency can be attributed to the joint effect of the augment of numbers of FITC acceptors within 10 nm from dispersed 117 to aggregated 5499 and the restricted rotational and translational motions of TPP-CDs donors and FITC acceptors. Ultimately, we successfully observe the fluctuations of ATP levels in the mitochondria using the aggregation-enhanced energy transfer strategy of the TPP-CDs-FITC nanodevice.

The selective deprotonation of carbon quantum dots for fluorescence detection of phosphate and visualization of latent fingerprints

We developed a water-soluble, stable and selective "turn-on" fluorescence sensing platform based on carbon quantum dots (CQDs) for rapid determination of phosphate (Pi) in aqueous solutions and for visualization of latent fingerprints on paper. The hydroxyl groups on the surface of the synthesized CQDs can be deprotonated by Pi to trigger the intramolecular charge transfer (ICT) process and the inhibition of excited-state proton transfer (ESPT), achieving a turn-on emission response. CQDs demonstrated the capability to selectively detect Pi over other common ions and biomolecules with the linear fluorescence intensity change in the range from 0 to 100 μM. Moreover, the paper sprayed with the CQD solution showed a remarkable blue emission speckle and a fingerprint upon addition of Pi solution and finger touching, respectively. Notably, the fingerprint images including level 3 details (crossover, bifurcation, termination, and island and sweat pores) are also clearly identified and distinguished, indicating their potential application in document security. We believe that the as-synthesized CQDs will provide a new tool for Pi detection in aqueous media and paper document security.

Production of photochromic nanocomposite film via spray-coating of rare-earth strontium aluminate for anti-counterfeit applications

New photochromic film was developed toward the preparation of anti-counterfeiting documents utilizing inorganic/organic nanocomposite enclosing a photoluminescent inorganic pigment and a polyacrylic binder polymer. To generate a translucent film from pigment/polyacrylic nanocomposite, the phosphorescent strontium aluminum oxide pigment should be well-dispersed in the solution of the polyacrylic-based binder without agglomeration. The photochromic nanocomposite was applied efficiently onto commercial cellulose paper documents utilizing the effective and economical spray-coating technology followed with thermofixation. A homogeneous photochromic film was immobilized onto cellulose paper surface to introduce a transparent film changing to greenish-yellow upon exposure to ultraviolet light as depicted by CIE coloration measurements. The photochromic effect was monitored at lowest pigment concentration (0.25 wt%). The spray-coated paper documents exhibit two absorbance bands at 256 and 358 nm, and two fluorescence peaks at 433 and 511 nm. The morphologies of the spray-coated documents were explored. The spray-coated paper sheets showed a reversible photochromic effect without fatigue under ultraviolet irradiation. The rheology of the produced photochromic composites as well as the mechanical properties and photostability of the spray-coated documents were studied.

Applications of Carbon Dots (CDs) in Latent Fingerprints Imaging

Carbon dots (CDs), a new member of the carbon-based material family, possess unique properties, such as high fluorescence, non-toxicity, eco-friendliness, stability and cost-effectiveness. These properties helped CDs to receive tremendous attention in various fields, namely, biological, opto-electronic, bio-imaging and energy-related applications. Although CDs are widely explored in bio-imaging and bio-sensing applications, their effectiveness in forensic science and technology is comparatively new. In this review, applications of CDs pertaining to latent FPs recovery since 2015 to 2020 is summarized comprehensively.

When rare earth meets carbon nanodots: mechanisms, applications and outlook

Rare earth (RE) elements are widely used in the luminescence and magnetic fields by virtue of their abundant 4f electron configurations. However, the overall performance and aqueous stability of single-component RE materials need to be urgently improved to satisfy the requirements for multifunctional applications. Carbon nanodots (CNDs) are excellent nanocarriers with abundant functional surface groups, excellent hydrophilicity, unique photoluminescence (PL) and tunable features. Accordingly, RE-CND hybrids combine the merits of both RE and CNDs, which dramatically enhance their overall properties such as luminescent and magnetic-optical imaging performances, leading to highly promising practical applications in the future. Nevertheless, a comprehensive review focusing on the introduction and in-depth understanding of RE-CND hybrid materials has not been reported to date. This review endeavors to summarize the recent advances of RE-CNDs, including their interaction mechanisms, general synthetic strategies and applications in fluorescence, biosensing and multi-modal biomedical imaging. Finally, we present the current challenges and the possible application perspectives of newly developed RE-CND materials. We hope this review will inspire new design ideas and valuable references in this promising field in the future.

Dual-functional lanthanide metal organic frameworks for visual and ultrasensitive ratiometric fluorescent detection of phosphate based on aggregation-induced energy transfer

Phosphate (Pi) not only plays a significant role in physiological processes, but also is an important indicator for aquatic ecosystems. The dual-functional lanthanide metal organic frameworks (MOFs) were synthesized for visual and ultrasensitive ratiometric fluorescent detection of Pi based on aggregation-induced energy transfer. In the MOFs material, ciprofloxacin (CIP) functions as an energy donor and results in the fluorescence enhancement of Eu³⁺; the introduction of pyromellitic acid can cause the aggregation of the CIP-Eu³⁺ complex, and red characteristic fluorescence of Eu³⁺ at 614 nm is further enhanced (about 40 times). When Pi is added to the MOFs solution, CIP is released from the MOFs, red fluorescence of Eu³⁺ is quenched and blue fluorescence of CIP is simultaneously recovered, thereby a ratiometric fluorescent probe for the detection of Pi was fabricated. The fluorescent response based on intermolecular energy transfer of the CIP-Eu³⁺ complex is very sensitive to Pi. The limit of detection (3σ/K) of the probe is ultrasensitive and attains 4.4 nM. The possible interferential substances such as 17 common metal ions and 14 anions investigated do not interfere with the Pi detection. The ratiometric fluorescent probe has been successfully used in the determination of Pi in real human urine and lake water samples. This work may supply a new strategy for fabricating ratiometric fluorescent probe and a prospective application in biological and environmental samples.

Polyol-Mediated Synthesis of Nitrogen-Containing Carbon-Dots from Tetracyanobenzene with Intense Red Fluorescence

Nitrogen-containing C-dots were prepared by heating (160 °C, 1 h) 1,2,4,5-tetracyanobenzene (TCB) in polyethylene glycol 400 (PEG400). The as-prepared monocrystalline C-dots were 2-4 nm in diameter and contained 24.4 wt. % of nitrogen. They showed intense fluorescence under excitation at 400-500 nm as well as under excitation at 600-700 nm. In addition to an excitation-wavelength-depending emission at 400 to 650 nm, the emission spectra exhibited a strong emission peaking at 715 nm, whose position was independent from the wavelength of excitation. For this deep-red emission a remarkable quantum yield of 69% was detected. The synthesis of nitrogen-containing C-dotswas completely performed in the liquid phase. Moreover, the C-dots could be directly dispersed in water. The resulting aqueous suspensions of PEG400-stabilized nitrogen-containing C-dots also showed intense red emission that was visible to the naked eye.