Blue-shifted Fluorescence Research Articles

Synthesis, fluorescence properties and structural characterization of two heteronuclear Zn(II)-Pr(III) clusters with a chain-shaped ether Schiff base ligand

Two new Zn(II)-Pr(III) heteronuclear clusters were synthesized by interfacial diffusion, [ZnPr(L)(NO3)2(OAc)(CH3OH)]·CH3CN (1) and [Zn4Pr2L4(terephthalate)2]·(NO3)2 (2) (H2L = bis(3-methoxysalicylaldehyde-3-oxopene-1,5-diamine). They have been characterized by elemental analysis, UV-Vis and IR spectroscopy, and single-crystal X-ray diffraction. Structural analysis revealed that 1 has a heterodinuclear structure, with Zn(II) in the inner cavity generated by deprotonated ligands L2- and Pr(III) in the larger outer cavity. Cluster 2 is a heterohexanuclear structure, in which the Pr(III) bridges two [ZnL] to form a heterotrinuclear secondary unit [Zn2PrL2], and then two terephthalates connect two secondary units to form a heterohexanuclear cluster structure. The solid-state fluorescence properties of clusters and ligand show that there are not only slightly blue-shifted fluorescence peak of ligand, but also characteristic fluorescence peaks of Pr(III) ions in the two clusters: 615 nm (3P0→3H6) for 1, 609 nm (1D2→3H4) and 646 nm (3P0→3F2) for 2, respectively. In the two clusters, the difference of ion fluorescence peaks is attributed to the symmetry difference of coordination geometric environment of Pr(III).

Fluorescence and photothermal dual-readout phthalocyanine-fluorescein conjugate for detection and photothermal sterilization of anaerobic bacteria

Anaerobic bacterial infection is a common but serious side-effect of dental implant, therefore, the development of new type of antimicrobials that can be applied in situ surgery area to avoid post-operation infection is highly desired. Herein, photothermal agent of silicon phthalocyanine-fluorescein conjugate, SiPc-FITC, is constructed via covalent bond. Comparing with the great majority of organic photothermal agents that based on H-aggregation induced nanocomposites requiring time-consuming uptake by bacteria as well as blue-shifted absorption and fluorescence quenching, SiPc-FITC demonstrates remarkable photothermal conversion efficiency in monomeric state (η = 29.0%) in aqueous solution along with favorable fluorescence emission, which not only significantly accelerate uptake rate of SiPc-FITC but also simplify clinic formulation process. Antibacterial experiments showed that both Gram-positive and Gram-negative anaerobic bacteria were completely eliminated within a few minutes when SiPc-FITC was mixed with bacteria and immediately irradiated with an 808 nm laser. As the results, SiPc-FITC is a multifunctional photothermal bactericide that can be used for fluorescence and photothermal dual readout in situ NIR photothermal sterilization to prevent post-operative infection for dental implant.

Charge transfer interactions exist in extracellular polymeric substances: Comparison with natural organic matter

Extracellular polymeric substances (EPS) and natural organic matter (NOM) are widely present in the environment. While the molecular basis of NOM's optical properties and reactivity after treatment with sodium borohydride (NaBH4) has been successfully explained by the charge transfer (CT) model, the corresponding structure basis and properties of EPS remain poorly understood. In this work, we investigated the reactivity and optical properties of EPS after NaBH4 treatment, comparing them to the corresponding changes in NOM. After reduction, EPS exhibited optical properties and a reactivity with Au3+ similar to NOM, manifesting an irreversible loss of visible absorption (≥70%) associated with blue-shifted fluorescence emission (8–11 nm) and a lower rate of gold nanoparticles formation (decreasing by ≥ 32%), which can be readily explained by the CT model as well. Furthermore, the absorbance and fluorescence spectra of EPS were solvent polarity dependent, contrary to the superposition model. These findings contribute to an original understanding of the reactivity and optical properties of EPS and facilitate further cross-disciplinary studies.

Topological effect on fluorescence emission of tetraphenylethylene-based metallacages

Herein, we describe the selective formation of a barrel-shaped or a ball-shaped fluorescent metallacage by controlling the shape and stoichiometry of the building blocks. Specifically, the tetraphenylethylene-based donor and two acceptors with different numbers of Pt(II) centers were combined via coordination-driven self-assembly. Owing to the differences in the shapes of the assemblies, the resultant ball-shaped metallacage displayed stronger and blue-shifted fluorescence compared to the barrel-shaped one in dilute solutions, while a reversal of fluorescence intensities was observed in the aggregation process. Overall, this work demonstrates that the photophysical properties of supramolecular coordination complexes can be affected by subtle geometrical factors, which can be controlled precisely at the molecular level.

Polymorphic triphenylamine derivative showing aggregation-induced emission and high-contrast mechanical force-induced blue shift

Mechanical force-induced, high-contrast blue-shift luminescent mechanochromic (MC) molecules have rarely been reported. Herein, we designed and synthesized an AIE luminogens (AIEgens) triphenylamine derivative N, N-diphenyl-4-(6-phenyl-[2,2′-bipyridin]-4-yl)aniline (DPTPA). Three different emission wavelengths from blue crystals (B-DPTPA), sky-blue crystals (S-DPTPA), and green crystals (G-DPTPA) were obtained by culturing the crystals under different crystallization conditions. All three crystal polymorphs showed high solid luminescent efficiency, each of which was sensitive to external pressure and was accompanied by significant fluorescence blue shift. Under a mechanical force, B-DPTPA shows a 12 nm blue shift, S-DPTPA fluorescence color changed from sky-blue to blue with an increase emission and G-DPTPA changed its color from green (510 nm) to sky-blue (428 nm) with an 82 nm blue shift. Such obvious color change and large blue shift were rarely been reported. Characterization of the photophysical properties, theoretical calculations, hydrostatic pressure, powder X-ray diffraction and X-ray single crystal structures showed that three crystal polymorphs of DPTPA originated from single molecules, space interactions, molecular pairs (dimers), and the blue shift of B-DPTPA, S-DPTPA, G-DPTPA were ascribed to the solid-state morphology transition from crystal to amorphous due to the destruction of space interactions and dimers. This study provides the relationship between the molecular packings and the blue shift emission of AIEgens materials under mechanical forces is understood in the molecular level.

Novel fluorescent probe for sequential recognition of Zn2+ and pyrophosphate in aqueous based on aggregation-induced emission

A new fluorescent probe (E)-4-(4-([2,2′:6′,2′'-terpyridin]-4′-yl)styryl)-1-dodecylpyridin-1-ium (TPy-SD), with the aggregation-induced emission (AIE) property in aqueous solution, has been synthesized and characterized. The new probe, TPy-SD exhibited excellent selectivity and sensitivity towards Zn2+ with a relatively low detection limit (1.76 × 10−7 M). The addition of Zn2+ is thought to disrupt the AIE property of TPy-SD, thereby leading to a fluorescence blue shift. Interestingly, the complex of probe TPy-SD with Zn2+ (Zn (II) TPy-SD), with molar ratio of 1:1, can be used as a simple, sensitive, and rapid means for the detection of pyrophosphates (PPi) in solution (water/DMSO = 99:1). As evidenced by transmission electron microscopy (TEM), dynamic light scattering (DLS) and fluorescence emission spectroscopy, this detection is thought to be due to the strong affinity between PPi and Zn2+, which brings out Zn2+ from the coordination cavity of chemical sensor TPy-SD, thus realizing the detection and recognition of PPi. Therefore, the new AIE fluorescent probe can be used as a dual probe for the detection of cations and anions.

Interactions of β-barrel assembly machinery protein D (BamD) with phospholipid bilayers.

The β-barrel assembly machinery (BAM) complex from Escherichia coli consists of the transmembrane protein BamA and four peripheral proteins, BamB, BamC, BamD and BamE. We investigated the lipid interactions of BamD (also called YfiO), which is essential for E. coli using site-directed fluorescence spectroscopy. To prepare a range of single-cysteine mutants of BamD for fluorescence labelling at the cysteine, we selected nine amino acid residues that were distributed over the entire surface of BamD. Expression plasmids were prepared and the mutants were then isolated from transformed E. coli strains to analyze interactions of BamD with bilayers composed of DLPC or of DLPG or of mixtures of DLPG and DLPE at a ratio of 4:1. BamD mutants were labeled with the fluorophore IANBD to examine BamD-lipid interactions by fluorescence spectroscopy. Higher fluorescence intensities and blue shifts of the emission spectra indicated that the entire surface of BamD interacted with the lipid bilayer. The fluorescence maxima of IANBD-labeled mutants were shifted towards shorter wavelength by ∼ 6 to 18 nm. Intensities of IANBD fluorescence increased most strongly for negatively charged DLPG bilayers, suggesting stronger binding due to electrostatic interactions. The weakest interactions were observed for lipid bilayers composed of DLPE and DLPG at a ratio of 4:1. For these bilayers, the IANBD-fluorescence spectra were most strongly changed for the IANBD labeled mutants A37C-BamD, G153C-BamD, and V181C-BamD. Fluorescence of all labeled mutants, except G200C-BamD, was quenched when 14-Doxyl-PC was used as a quencher, indicating penetration of BamD into the lipid bilayer. Fluorescence spectra of L75C-BamD and of V181C-BamD also indicated interactions with BamA in the absence of lipid bilayers.

Characterization of unexpected blue-shifted single molecule fluorescence of JF646 and JF669 for SMLM.

JF-Halotag dyes have become increasingly popular for single-molecule localization microscopy (SMLM) because of their favorable photo-physics, ease of use, and compatibility with live-cell imaging. However under a variety of conditions, the excitation and emission wavelengths from individual emitters can deviate significantly from the commonly accepted characterization, leading to artifacts in two color SMLM data. Here I show results from multiple in vivo and in vitro experiments demonstrating 640nm mediated photo switching of JF669 from a conventional far-red signal to a 561nm excitable red single molecule signal. This result is exciting because it enables UV-free PALM experiments. UV radiation causes cell death, increases auto fluorescence, and induces cell stress, which may affect the behavior of labeled proteins or cellular processes of interest. Additionally, I present evidence of a subpopulation of JF646 molecules that can be excited by 561nm light, but emit red instead of far-red light. This unexpected fluorescence causes single molecule cross talk in the red channel, despite the commonly accepted characterization. This phenomenon is more apparent at low dye concentrations as well as high temperatures, suggesting that a self-interaction between JF646 molecules may bias the well characterized fluorescence, while in isolation JF646 may have significantly blue-shifted excitation and emission spectra. Together, these results show potentially useful photo-physical behavior of JF dyes, but also highlight the importance of careful controls when using synthetic dyes for single molecule localization microscopy.

Solvothermal synthesis and device fabrication of a Eu3+-based metal-organic framework as a turn-on and blue-shift fluorescence sensor toward Cr3+, Al3+ and Ga3.

A novel three-dimensional Eu3+-based metal-organic framework with the formula {[(CH3)2NH2][Eu(BTDI)]·H2O·DMF}n (JXUST-25) was prepared by solvothermal method based on Eu3+ and 5,5'-(benzothiadiazole-4,7-diyl)diisophthalic acid (H4BTDI) with benzothiadiazole (BTD) luminescent groups. Due to the presence of Eu3+ and organic fluorescence ligand, JXUST-25 displays turn-on and blue-shift fluorescence toward Cr3+, Al3+ and Ga3+ with limits of detection (LOD) of 0.073, 0.006 and 0.030 ppm, respectively. Interestingly, the alkaline environment can change the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+ and the addition of HCl solution realizes the reversible change of the fluorescence of JXUST-25 toward Cr3+/Al3+/Ga3+. It is noteworthy that the fluorescent test paper and light-emitting diode lamp based on JXUST-25 can effectively detect Cr3+, Al3+ and Ga3+ by the visual changes. In addition, the turn-on and blue-shift fluorescence between JXUST-25 and M3+ ions may be caused by the host-guest interaction and the absorbance caused enhancement mechanism.

Structure-activity relationship of dietary flavonoids on pancreatic lipase

Lipase is a very important digestive enzyme for triglyceride absorption in vivo. The inhibitory activities of 26 dietary flavonoids, including flavone, flavanone, isoflavone and flavanol, on lipase were determined. Flavone exhibited stronger inhibitory activity than other types of flavonoids. Among them, luteolin exhibited the strongest inhibitory activity with IC50 value of 99 ± 11 μM, followed by quercetin and baicalein. The binding affinity of these flavonoids with lipase was investigated by fluorescence titration method. The binding affinity of flavones was stronger than flavanones, and was linearly positively correlated with their inhibitory activity. The binding of flavones on lipase caused the blue-shift of fluorescence, while flavanones caused red-shift. The analysis of structure-activity relationship of flavonoids on lipase revealed that the structure of C ring is very crucial. The hydrogenation of C2=C3 bond and the absence of C=O group in C ring both caused significant decrease of inhibitory activity. Besides, the hydroxylation on ring A and B of flavones increased the activity, while glycosylation weakened the activity. Molecular docking analysis confirmed that C2=C3 bond in C ring of flavones increases the π-conjugation and contributes to maintaining the planarity of flavonoid structure, which favour its Pi-Pi interaction with lipase.

A NIR BODIPY-based ratiometric fluorescent probe for HClO detection with high selectivity and sensitivity in real water samples and living zebrafish

Hypochlorous acid (HClO) plays an important role in many physiological and pathological activities. In this work, a novel BODIPY-based Near-infrared (NIR) ratiometric fluorescent probe BODIPY-Hyp was designed for the rapid detection of HClO. The probe BODIPY-Hyp was highly selective and sensitive for HClO with a low detection limit of 16.74 nM and short response time of less than 60 s. The probe BODIPY-Hyp in response to HClO exhibited a significant blue-shifted fluorescence emission from 700 nm to 530 nm, and its fluorescence intensity ratio (I530 nm/I700 nm) increased about 1200 times before and after adding HClO. Moreover, the reaction mechanism of BODIPY-Hyp with HClO was verified by HRMS analysis, 1H NMR titration and DFT calculations. Furthermore, BODIPY-Hyp was successfully processed into a portable test strip-based device for the detection of HClO. In addition, the probe BODIPY-Hyp could be used in real time to monitor the levels of HClO in living zebrafish larvae. In conclusion, BODIPY-Hyp has great application potential in the life and environmental sciences.

Significant Promotion of Light Absorption Ability and Formation of Triplet Organics and Reactive Oxygen Species in Atmospheric HULIS by Fe(III) Ions.

Metal ions are key components in atmosphere that potentially affect the optical properties and photochemical reactivity of atmospheric humic-like substances (HULIS), while this mechanism is still unclear. In this study, we demonstrated that atmospheric HULIS coupled with Fe3+, Cu2+, Zn2+, and Al3+ exhibited distinct optical properties and reactive intermediates from that of HULIS utilizing three-dimensional fluorescence spectroscopy and electron paramagnetic resonance spectroscopy. The HULIS components showed light absorption that increased by 56% for the HULIS-Fe3+ system, fluorescence blue shift, and fluorescence quenching, showing a certain dose-effect relationship. These are mainly attributed to the fact that the highly oxidative HULIS chromophores have a stronger complexing ability with Fe3+ ions than the other metal ions. In addition, triplet organics (promoting ratio: 53%) and reactive oxygen species (promoting ratio: 82.6%) in the HULIS-Fe3+ system showed obvious generation promotion. Therefore, the main assumption of the photochemical mechanisms of atmospheric HULIS in the HULIS-Fe3+ system is that Fe3+ ions can form 3HULIS*-Fe3+ complexation with photoexcited 3HULIS* and then transition to the ground state through energy transfer, electron transfer, or nonradiative transition, accompanied by the formation of singlet oxygen and hydroxyl radicals. Our results provide references for evaluating the radiative forcing and aging effect of metal ions on atmospheric aerosols.

An Acid-triggered Reactive and Enhanced Fluorescent Probe for Selective Detection of Al3+/H+ and its Application in Real Water Samples and Living Cells.

A reactive fluorescent "turn-on" probe (di-PIP) with imine-linked dual phenanthro[9,10-d]imidazole luminophore have been conveniently prepared as an Al3+ and H+ dual functional receptor. di-PIP displayed high selectivity and sensitivity towards Al3+ ion in DMF/HEPES accompanied by fluorescence blue-shift and a good linear relationship as well as a low detection limit of 30.5nmol·L-1, which can root from the synergetic functions of the decomposition reaction of di-PIP promoted by acidic Al3+ and the coordination effect between decomposition product and Al3+. Intriguingly, it was found that hydrogen ion H+ can be sufficient for simulating the fluorescence enhancing of di-PIP. 1H NMR titration and MS analyses for elucidation of the intermediate structure further revealed that the acid-triggered decomposition reaction resulted in the rapid, and sensitive sensing to Al3+ and H+. In addition, the probe di-PIP could be successfully applied to the detection of Al3+ in real water samples, and also utilized to visualize Al3+ and H+ in the living cells.

Water-soluble dual lysosome/mitochondria-targeted fluorescent probe for detection of SO2 in water, food, herb, and live cells

In this paper, we present a new donor-π bridge-acceptor type fluorescent probe, MIB, which bears two organelle-targeted groups, namely positively charged benzothiazole group for mitochondria and morpholine moiety for lysosomes. In aqueous solution, the nucleophilic addition of HSO3- (as SO2 donor) to MIB blocked its long-range π-conjugation and ICT process and resulted in significant optical signal changes (blue-shifted UV absorbance and fluorescence), which enabled colorimetric and ratiometric fluorescent detection of HSO3- with high selectivity and sensitivity (detection limit of 63.15 nM). MIB offers obvious advantages of good water-solubility, fast response time (within 1 min), unique dual lysosome/mitochondria targeting capability and has been applied to the sensing of endogenous and exogenous SO2 in live cells through fluorescent imaging. In addition, the proposed probe has been utilized for the determination of bisulfite in real water, food and herbal medicine samples, showing good recovery (91.45 % − 109.3 %) and precision.

A pH-Stable TbIII-Based Metal-Organic Framework as a Turn-On and Blue-Shift Fluorescence Sensor toward Benzaldehyde and Salicylaldehyde in Aqueous Solution.

A new polydentate tetracarboxylic acid with a benzothiadiazole unit (4',4'''-(benzo[c][1,2,5]thiadiazole-4,7-diyl)bis([1,1'-biphenyl]-3,5-dicarboxylic acid), H4BTDBA) has been used to prepare a pH-stable three-dimensional TbIII-based metal-organic framework (MOF) with the formula {[(CH3)2NH2]0.7[Tb2(BTDBA)1.5(lac)0.7(H2O)2]·solvents}n (Hlac = lactic acid, JXUST-19). JXUST-19 exhibits a new (4,4,12)-connected topology based on tetranuclear [Tb4] clusters. JXUST-19 can remain stable when soaked in water for at least 1 week and in aqueous solutions with various pH values (2-12) for 24 h. Fluorescence study indicates JXUST-19 can be employed as a rare turn-on and blue-shift MOF sensor toward benzaldehyde (BZ) and salicylaldehyde (SA). To date, JXUST-19 represents the first TbIII-based turn-on MOF sensor toward salicylaldehyde in aqueous solution, and the fluorescence enhancement and naked-eye detection of BZ have been rarely reported. In addition, JXUST-19 based fluorescent test papers, light-emitting diode lamp beads, and portable composite films were developed to realize naked-eye detection of BZ and SA, which has great potential in practical applications.

Fabrication of sulfur quantum dots via a bottom-up strategy and its application for enhanced fluorescence monitoring of o-phenylenediamine

Nowadays, the synthesis of luminescent sulfur quantum dots (SQDs) mainly depends on a top-down method, which requires abnormally long reaction time by etching bulk sulfur powder. To overcome this limitation, a facile bottom-up strategy has been provided to fabricate fluorescent SQDs enabled by the reaction between thioacetamide (TAA) and hydrogen peroxide (H2O2) using carboxymethyl cellulose (CMC) as a passivation agent. Herein, TAA acts as sulfur source to release sulfide ions (S2-), which react directly with H2O2 to generate element sulfur to assemble the CMC-stabilized SQDs (SQDs@CMC). The prepared SQDs@CMC emits blue fluorescence, and owns good water dispersibility, superior photostability, excitation dependent luminescence and a reasonable quantum yield up to 9.31 %. Herein, the prepared SQDs@CMC combined with Cu2+ has a sensitive response toward o-phenylenediamine (OPD) by forming ternary SQDs@CMC/Cu2+/OPD complex, which can emit enhanced blue-shift fluorescence. The fluorescence of the ternary complex is 10 times higher than that of SQDs@CMC and the proposed SQDs@CMC-Cu2+ assembly has been successfully used to monitor OPD in various waters with high selectivity. Therefore, this paper not only provides a bottom-up strategy to prepare SQDs, but also develops a novel fluorescence “turn on” sensing platform for OPD detection.

A lead selective dimeric quinoline based fluorescent chemosensor and its applications in milk and honey samples, smartphone and bio-imaging

Dimeric quinoline-based Schiff base was developed (DQS) for the specific detection of Pb2+ ion via fluorimetry. DQS coordinates with Pb2+, a variation in fluorescence intensity with enhanced radical blue shift was observed due to the restriction of CN rotation, CN isomerization, and photoinduced electron transfer (PET) mechanisms. In addition, the intramolecular charge transfer (ICT) from electron-donating morpholine to phenylene diamine acceptor linked quinoline bridge is responsible for the blue-shifted fluorescence enhancement in the DQS-Pb2+ complex. The binding stoichiometry of DQS: Pb2+ (1:2) was confirmed by host–guest titration and mass spectrometry. The limit of detection (LOD) of the DQS was found to be 1.3 × 10-7 M for Pb2+ ion. The DQS sensing ability of Pb2+ was further applied into milk and honey samples, smartphone, bio-imaging and to construct of an INHIBIT molecular logic gate.

Blue-shifted and naked-eye recognition of H2PO4− and acetylacetone based on a luminescent metal−organic framework with new topology and good stability

Fluorescence detecting both organic and inorganic analytes has aroused tremendous scientific interests, because fluorescence techniques have high sensitivity and are easy to operate. A new three-dimensional (3D) MOF {[(CH3)2NH2][Zn3(bbip)(BTDI)1.5(OH)]·DMF·MeOH·3H2O}n (JXUST-13, bbip = 2,6-bis(benzimidazol-1-yl)pyridine and H4BTDI = 5,5′-(benzo[c][1,2,5]thiadiazole-4,7-diyl)diisophthalic acid) with new 4,4,8-connceted topology has been successfully synthesized and structurally characterized. Importantly, JXUST-13 could recognize H2PO4− and acetylacetone (Acac) by obvious fluorescence blue shift and slight enhancement with the detection limits of 2.70 µmol/L and 0.21 mmol/L, respectively. In addition, JXUST-13 exhibits relatively good thermal stability, chemical stabilities as well as reusability, and the analytes could be distinguished by naked eye and fluorescence test paper. Remarkably, JXUST-13 is the first dual-responsive MOF sensor based on fluorescence blue shift for the detection of H2PO4− and Acac with good selectivity in a handy, economic, and environmentally friendly manner.

Multiple fluorescence color transitions mediated by anion-π interactions and C-F covalent bond formation

The emission changes of fluorescent dyes under the influence of environmental changes or interaction with analytes are the basis for designing ratiometric fluorescent probes and logic gates. However, it is rare that only one external stimulus induces continuous fluorescent color changes in a fluorescent dye. In this paper, we report a cage-like molecule formed by two benzene rings and three imidazolium salts which produces continuous fluorescence wavelength changes when interacted with fluoride ions. Fluoride ions are first bound to the center of the cage under the action of anion-π interaction, and the (C−H)+···F– type ionic hydrogen bonds induce the blue-shift of fluorescence. The subsequent formation of C-F covalent bonds with fluoride ions makes the fluorophore wavelength continue to blue-shift, and finally obtains continuous multiple fluorescence changes caused by a single external stimulus. According to the fluorescence wavelength and intensity, six different fluorescence signal channels can be obtained, which can be encoded as six numbers from 0 to 5. We expect that this reaction process can find applications in quantitative anion recognition and molecular counters.

Selective antibacterial activity of a novel lactotransferrin-derived antimicrobial peptide LF-1 against Streptococcus mutans

ObjectiveStreptococcus mutans is a key pathogen involved in the development of caries lesions. Previously, we developed a novel lactotransferrin-derived antimicrobial peptide LF-1 with potential selective activity against S. mutans. This study aimed to further confirm the selectivity of LF-1 by investigating its effect on S. mutans membrane. DesignThe effects of LF-1 on the viability of human gingival fibroblasts (HGFs) and three common oral Streptococcus (S. mutans, S. sanguinis, and S. gordonii) were evaluated and its structural characteristics were analysed using eukaryotic and prokaryotic membrane-simulated liposomes. Membrane affinity of LF-1 to the three streptococci strains was evaluated using the 3',3'-dipropylthiadicarbocyanine iodide experiment, hydrophobicity assay, and flow cytometry analysis. Transmission electron microscopy (TEM) was used to observe morphological changes in the three streptococcal membranes after LF-1 treatment. ResultsLF-1 displayed lower cytotoxicity to HGFs and selective antibacterial activity against S. mutans. LF-1 exhibited a typical α-helix structure and showed a tryptophan fluorescence blue shift in the prokaryotic membrane-simulated model. The most notable LF-1 induced changes occurred in the membrane potential and hydrophobicity of S. mutans among the three streptococci strains. Furthermore, the fluorescence of fluorescein isothiocyanate-labelled LF-1 was higher in S. mutans than in the other species. TEM showed that 16 μmol/L LF-1 could induce mesosome-like structures in S. mutans, whereas no significant morphological changes occurred in the other species. ConclusionLF-1 has selective affinity for and antibacterial activity against S. mutans with strong membrane disrupting ability, highlighting the potential of LF-1 as a crucial antibacterial agent in caries prevention.