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Surface-enhanced Raman spectroscopy (SERS) coupled with density functional theory (DFT) computations can characterise the adsorption orientation of a molecule on a nanoparticle surface. When using DFT to simulate SERS on a silver surface, one typically employs an atom (Ag), ion (Ag+), or cluster (Agx or Agx+) as the model surface. Here, by examining the nucleobase 2,6-diaminopurine (2,6-DAP) and then generalising our strategy to three other molecules, we show that employing silver oxide (Ag2O) as the model surface can quantitatively improve the accuracy of simulated SERS.

8-Azaadenine (8AA) is structurally similar to both adenine and benzotriazole, and therefore, it is reasonable that it could adsorb onto noble metal nanoparticles (NPs) in an orientation analogous to either one. In this study, Raman and surface-enhanced Raman spectroscopy (SERS) of 8AA are investigated to determine its adsorption orientation on Ag NPs. In support of the analysis, the Raman spectra of 8AA and various Ag+/8AA complexes were simulated using density functional theory (DFT) at the B3LYP level. For both normal Raman and surface-enhanced Raman spectroscopy, good agreement is observed between the experimental and simulated spectra. Our findings show that 8AA adsorbs onto Ag NPs via its N3 and N9 atoms side in an adenine-like manner. This result may be useful for nanoparticle-mediated drug delivery strategies of 8-azapurines or similar molecules with biological activities.

This study describes a bottom-up assembly route for monodisperse carbon dots (CDs) into different sizes of CD aggregates through the control of the concentration of fatty acids. The highly monodisperse CDs were prepared via solvent-thermal treatment of edible soybean oil, which generated glycerol-based polymer as a carbon source and fatty acid as a surface capping in the synthetic process. The as-synthesized CDs exhibited small particle size variation (2.7 ± 0.2 nm) and narrow emission bands (full width at half-maximum20 nm). The monodisperse CDs can self-assemble into blue-, green-, yellow-, and red-emitting CD aggregates by tuning the concentration of fatty acids. Compared to commercially available organic dyes and semiconductor quantum dots, the CD aggregates provided a 10-7000-fold improvement in brightness. Additionally, their emission wavelength was tunable across the entire visible spectrum by tuning the excitation wavelength. Because of their high brightness, fluorescence imaging of a single carbon dot and CD aggregate was simply achieved using filter-free dark-field fluorescence microscopy (DFM). We also demonstrate the use of filter-free DFM to dynamically image cellular uptake of the monodisperse CDs in MCF-7 cells and Huh-7 liver cancer cells. Without the conjugation of the fluorophore to the CDs, the particle aggregation-induced red-shifted emission enables the development of the CD-based ratiometric sensor for Fe

Different-sized carbon dots (CDs) with full-color emissions have immerse potentials as a novel class of light source in the field of light-emitting diodes (LED). However, few studies have been devoted to the development of the one-step process for preparing white-light-emitting CDs (WLECDs). Herein, we present a facile and one-pot synthesis of the WLECDs through microwave-assisted hydrothermal carbonization of poly(diallyldimethylammonium chloride) (PDDA). The as-synthesized WLECDs had a round shape with a mean particle size of 2.22 nm and their zeta potential reached up to 47 mV. Fourier transform infrared spectroscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy revealed the appearance of nitrogen and oxygen-containing functional groups on the CD surface, generating many surface state emissive traps. Additionally, photoluminescence spectroscopy showed that the CDs exhibited excitation-dependent surface-state emission and excitation-independent core-state emission. When excited at 350 nm, an aqueous solution of the WLECDs emitted white light with an absolute quantum yield of 11% and a correlated color temperature of 5999 K at Commission International de l'Eclairage (CIE) coordinates of (0.321, 0.348). Single-particle photoluminescence spectroscopy demonstrated that the WLECDs still possessed broadband white-light emission from 400 to 800 nm at a single particle level. Furthermore, a white-light-emitting polymer composite film excited by 365-nm UV light was fabricated by embedding the WLECDs into a polyvinyl alcohol matrix. This flexible solid-state film showed a correlated color temperature of 7023 K at CIE coordinates of (0.303, 0.332) and. Given that the WELCDs have highly positive charges, the fabrication of a white-light-illuminating film was successfully conducted by layer-by-layer assembly of the WELCD and poly(4-styrenesulfonic acid).

Simple, low-cost, rapid, selective, and sensitive sensing kits are required for screening of illicit date rape drugs such as nimetazepam, flunitrazepam, clonazepam, and nitrazepam in beverages. Because of low solubility of these analytes in aqueous solution, hydrophobic carbon dots (hC-dots) are needed. In this study, hC-dots are prepared from D-phenylalanine through a hydrothermal route, which have been used for screening of the analytes. To minimize matrix interference in various beverages, including beer, red wine, whisky, and orange juice, liquid-liquid extraction of the analytes using toluene for 5 min is required before quantitation based on analyte induced fluorescence quenching of the hC-dots at 430 nm when excited at 365 nm. This assay allows the quantitation of nimetazepam down to 7.24 μM, which is lower than that found in the beverages associated with drug-facilitated sexual assault (DFSA). The assay is selective toward nitro-substituted benzodiazepines over popular abused drugs, including 4-chloroethcathinone, cocaine, heroin, 4-hydroxybutyric acid, ketamine, and methamphetamine. Since only hC-dots (dispersed in 0.5 mL toluene), a handheld UV light (365 nm), and a camera (or smartphone) are required, this simple, low-cost, rapid, and selective sensing system is ideal for beverage analyses at DFSA crime scenes.

Thiol-induced core etching of gold nanoparticles is a general method for the production of gold nanoclusters (AuNCs) of various sizes. This paper is the first report on the efficient reaction of glutathione-capped gold nanoparticles (GSH-AuNPs) with hydroxyl radicals to produce oligomeric AuI–thiolate complexes at ambient temperature. Also, hydroxyl radicals can etch commercially available gold nanoparticles (100 nm); this strategy can be applied for the removal of gold from scrap electronics. Additionally, proteins can trigger the aggregation of oligomeric AuI–thiolate complexes under neutral conditions resulting in the formation of fluorescent AuNCs. For example, the reaction of trypsin, lysozyme, and glucose oxidase with oligomeric AuI–thiolate complexes produces Au5, Au8, and Au13 clusters with emission maxima at 415, 460, and 535 nm, respectively. Interestingly, trypsin- and glucose oxidase-stabilized AuNCs could sense GSH and glucose via GSH-induced etching of AuNCs and H2O2-mediated oxidation of AuNCs, respectively.

In this work, we report a highly sensitive colorimetric sensing strategy for cancer biomarker diagnosis using gold nanoparticles (AuNPs) labeled with biotinylated poly(adenine) ssDNA sequences and streptavidin-horseradish peroxidase for enzymatic signal enhancement. By adopting this DNA-AuNP nanoconjugate sensing strategy, we were able to eliminate the complicated and costly thiol-binding process typically used to modify AuNP surfaces with ssDNA. In addition, different antibodies can be introduced to the AuNP surfaced via electrostatic interactions to provide highly specific recognition sites for biomolecular sensing. Moreover, multiple, simultaneous tests can be rapidly performed with low sample consumption by incorporating these surface-modified AuNPs into a paper-based analytical device that can be read using just a smartphone. As a result of these innovations, we were able to achieve a detection limit of 10 pg/mL for a prostate specific antigen in a test that could be completed in as little as 15 min. These results suggest that the proposed paper platform possesses the capability for sensitive, high-throughput, and on-site prognosis in resource-limited settings.

Carbon-dot (C-dot) liposome consisting of several thousands of C-dots shows interesting photoswitching properties. The water-dispersible C-dot liposome possesses intrinsic photoluminescence (PL) and is stable against salt and photoirradiation. The PL of C-dot liposome can be turned off and then on under photoirradiation over the wavelength regions of 510–540 nm and 365–420 nm, respectively. Like reported C-dots, the C-dot liposome emits various colors when excited at different wavelengths. Having great stability and high contrast, images of individual C-dot liposome have been recorded, showing negligible photoblinking. Through a simple photolithographic approach, micropatterns of C-dot liposomes emitting different colors have been fabricated.

We present a simple, one-pot approach for synthesizing ultrafine platinum (Pt) nanoclusters (NCs) under alkaline conditions using lysozyme (Lys) as a template. From the analysis of the nanoclusters by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, Lys VI-stabilized Pt NCs majorly consisted of Pt4 clusters. The formation of Pt NCs was confirmed using X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy. The maximal fluorescence of Pt NCs appears at 434 nm with a quantum yield of 0.08, a fluorescence lifetime of 3.0 ns, and excitation-dependent emission wavelength behavior. Pt NCs exhibit an intrinsic oxidase-like activity because Pt NCs can catalyze O2 oxidation of organic substrates through a four-electron reduction process. Compared with larger Pt nanoparticles, the Pt NCs produce substantially greater catalytic activity in the O2-mediated oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid), 3,3',5,5'-tetramethylbenzidine, and dopamine.

Core etching of gold nanoparticles (AuNPs) into smaller-sized clusters is a classic method for fabricating gold nanoclusters (AuNCs). The top down-based synthesis of AuNCs includes two steps: (i) reducing the Au(3+) precursor solution to generate AuNPs in the presence of protecting ligands and (ii) core etching of the formed AuNPs into the AuNCs via ligand exchange. For the first time, this paper describes a one-step approach for preparing AuNCs using a top down approach. The sinapinic acid (SA)-induced formation of the AuNCs involved a three-step reaction process. First, large AuNPs (200 nm) were quickly formed after mixing SA and the Au(3+) precursor solution. Second, excess SA molecules self-assembled on the NP surface, and large AuNPs were etched to small AuNPs via electrostatic repulsion between the neighboring SA molecules. Finally, SA-induced core etching of the AuNPs resulted in the formation of the AuNCs within 70 min. Furthermore, we showed that the presence of the AuNCs in SA was capable of suppressing crystal growth and eliminating the coffee-ring effect. Thus, proteins can be successfully quantified using the SA-AuNCs as matrices for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Compared with using SA as matrices, the SA-AuNCs offered substantial advantages for improving shot-to-shot reproducibility and enhancing the ionization efficiency of proteins.

This study reported that lysozyme Type VI (Lys VI)-stabilized Au8 clusters serve as a model to probe how distinct types of alkanethiol ligands affect the core etching of AuNCs. By monitoring the fluorescence of Au8 clusters, we determined that thioglycolic acid (TGA)-induced core etching of Au8 clusters was substantially faster at pH 9.0 than it was at pH 3.0. This can be attributed to more efficient electron injection from TGA to Au8 clusters at pH 9.0, facilitating the core etching of Au8 clusters. Because long-chain mercaptoalkanoic acids attached to Au8 clusters are considerably disordered and exhibit a high density of gauche defects, the ability of mercaptoalkanoic acid to etch Au8 clusters increased when the alkyl chain length was decreased. The thiol analogs exhibited the following trend in the core etching of Au8 clusters at pH 9.0: TGA > 2-mercaptoethanol > 1-octanethiol. These results indicate that the carboxyl group of ligand is a key element for the core etching of Au8 clusters. We also disclosed that Au8 clusters can protect Lys VI activity against denaturation and act as a fluorescent probe to detect thimerosal in vaccines.

3-Methyladenine and 7-methyladenine are biomarkers of DNA damage from exposure to methylating agents. For example, the concentration of 3-methyladenine increases significantly in the urine of cigarette smokers. Surface-enhanced Raman spectroscopy (SERS) has shown much potential for detection of biomolecules, including DNA. Much work has been dedicated to the canonical nucleobases, with comparatively fewer investigations of modified DNA and modified DNA nucleobases. Herein, Raman spectroscopy and SERS are used to examine the adsorption orientations of 3-methyladenine and 7-methyladenine on Ag nanoparticles. Density functional theory (DFT) calculations at the B3LYP level are used to support the conclusions via simulated spectra of the nucleobases and of Ag+/nucleobase complexes. The results herein show that 7-methyladenine adsorbs upright via its N3 and N9 atoms side, similarly to adenine. 3-Methyladenine adsorbs in a very tilted or flat orientation on the Ag nanoparticles. These findings will be useful for future SERS or other nanoparticle-based bioanalytical assays for detection of these methyladenines or other modified nucleobases.

This paper presents a one-pot approach for preparing highly fluorescent Au(8) clusters by reacting the Au(3+) precursor solution with lysozyme type VI (Lys VI) at pH 3. The fluorescence band of (Lys VI)-stabilized Au(8) clusters is centered at 455 nm on the excitation at 380 nm. Blue-emitting Au(8) clusters have a high quantum yield (∼56%), two fluorescence lifetimes, and a rare amount of Au(+) on the surface of the Au core. When the pH of a solution of Au(8) clusters increases suddenly to 12, the Au(8) clusters gradually convert to Au(25) clusters over time. This conversion is also observed in the case of (Lys VI)-directed synthesis of Au(25) clusters at pH 12. The pH-induced conversion of Au(8) to Au(25) clusters suggests that the size of (Lys VI)-stabilized gold nanoclusters (AuNCs) relies on the secondary structure of Lys VI, which is susceptible to pH change. Based on these results and previous literature, this paper proposes the possible mechanism for growing (Lys VI)-stabilized Au(8) and Au(25) clusters. Additionally, (Lys VI)-stabilized Au(8) clusters could sense glutathione (GSH) through GSH-induced core-etching of Au(8) clusters; the limit of detection at a signal-to-noise ratio of 3 for GSH is determined to be 20 nm. Except for cysteine, the selectivity of (Lys VI)-stabilized Au(8) clusters for GSH over amino acids is remarkably high. The practicality of using Au(8) clusters to determine the concentration of GSH in a single drop of blood is also validated.

Objective: Muscle mass loss, muscle strength decline and poor physical performance, slow gait speed and decreased mobility are characteristics of sarcopenia and the frailty syndrome. Frailty is a dynamic state and it may transit with aging. The purpose of this study was to examine the changes and associations among lower extremity muscle mass and muscle strength observed longitudinally for 3 years in robust and pre-frail outpatient older adults. Methods: This was a 3-year longitudinal cohort study of outpatient older adults recruited from geriatric clinics. Frailty status was characterized according to Fried's Frailty Phenotype. Predicted muscle mass (PMM) of lower extremity was measured by bioelectrical impendence analysis (Tanita BC-418 Pro Segmental Body Composition Analyzer). Cybex Norm dynamometer was used to measure knee extensors and flexors isokinetic muscle strength at 0, 60, and 180 degrees/second. Physical performance was assessed by the 5-times sit-to-stand test (5tSTS), timed up and go test (TUGT) and 5-meter walk test (5MmWT). Data were collected annually and then analyzed by analysis of variance (ANOVA) and Pearson correlation. Results: Overall, 95 subjects (49 males, 46 females) completed all three follow-up examinations. The mean age was 77.48 (±5.79) years. There were 26.3% of subjects in the robust and 73.7% in the pre-frail status. The PMM was significantly decreased in robust older adults (p=0.04), the isokinetic muscle strength of knee extensors at 180 degrees/second decreased significantly both in robust (p=0.005) and pre-frail (p=0.002) group. Regarding physical performance, TUGT was significantly worse in follow up from baseline in both groups (robust p=.05; pre-frail p＜0.001). The change of TUGT from baseline to follow up correlated significantly with the change of isokinetic muscle strength of knee extensors at 0 degrees/second (r=.23, p=0.024). Conclusion: Knee extensor muscle strength was critical for detecting the ageing related changes of muscle strength in robust and pre-frail outpatient older adults. Furthermore, it was significantly related to the ability to stand up, walk, and turn.

This paper presents a discussion of a one-pot approach for preparing lyszoyme type VI (Lys VI) stabilized clusters, including small (Au 7 Ag and Au 8 ) and large (Au 24 Ag) clusters, for ratiometric fluorescence sensing of Hg 2+ . Our previous study (Chen and Tseng, Small 8 (2012) 1912) showed the formation of intermediate Au 8 clusters in the conversion of Au + –Lys VI protein complexes to Au 25 clusters. The presence of Ag + in the precursor solution slowed this conversion, thereby forming two-sized clusters. With an increase in Ag + content, a systematic blue shift in the first exciton absorption and fluorescence peaks indicated the formation of Au–Ag bimetallic clusters. The prepared Ag + /Au 3+ molar ratio of 2:8 resulted in the formation of two-sized clusters, with dual emission bands centered at 471 and 613 nm. After these clusters are separated by a membrane filter, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to determine the composition of Au 24 Ag clusters. By monitoring the intensity ratio of the two emission wavelengths, the solution consisting of Hg 2+ -insensitive small clusters (Au 7 Ag and Au 8 ) and Hg 2+ -sensitive Au 24 Ag clusters exhibited a ratiometric fluorescence response toward Hg 2+ , and provided a built-in correction for photobleaching; the limit of detection at a signal-to-noise ratio of three for Hg 2+ was estimated to be 1 nM. This probe was successfully applied to ratiometric fluorescence sensing of Hg 2+ in tap water.

This study develops a novel and high performance colorimetric probe for dopamine (DA) detection. Aqueous-phase gold nanoparticles (AuNPs) extracted with 4-(dimethylamino) pyridine (DMAP) from toluene solvent is used as the reaction probes. The conjugated AuNPs of the diameter around 13 nm disperse into the size of 2–5 nm while adding dopamine (DA), resulting in the color change of the AuNPs solution from red to green. Therefore, the extracted AuNP solution can be a good indicator for detecting DA biosample. Transmission electron microscope (TEM) observations and dynamic light scattering (DLS) tests show that the AuNPs turn into smaller size right after adding DA. Results confirm that the DMAP capped AuNPs are etched by the DA molecules due to the stronger affinity between DA and AuNPs and thus cause a blue shift in the absorption spectrum. The concentration of dopamine is quantitatively monitoring using an UV-vis spectrometer with a limit of detection (LOD) of lower than 5 nM. The developed AuNPs etching protocol for dopamine detection provides a novel and versatile approach for rapid biosensing applications.

This study develops a novel and high performance colorimetric probe for dopamine (DA) detection. Aqueous-phase gold nanoparticles (AuNPs) extracted with 4-(dimethylamino)pyridine (DMAP) from toluene solvent are used as the reaction probes. The original AuNPs of diameter around 13 nm separate into 2-5 nm sizes when dopamine (DA) is added, resulting in the color change of the AuNP solution from red to blackish green. Transmission electron microscopy (TEM) observations and dynamic light scattering (DLS) tests show that the AuNPs break into their smaller sizes right after addition of DA. The results confirm that the DMAP capped AuNPs are etched by the DA molecules due to the strong affinity between DA and AuNPs, thus causing a blue shift in the absorption spectrum. The concentration of DA is quantitatively monitored by using a UV-Vis spectrometer with a limit of detection (LOD) as low as 5 nM. In addition, the results also show that the methods developed appear to have no significant problems in detecting DA in the sample even with the presence of (10 mM) common interferents such as ascorbic acid (AA), homovanillic acid (HVA), catechol (CA) and glutathione (GSH). The developed AuNP etching protocol for dopamine detection provides a novel and versatile approach for rapid biosensing applications.

Transition metal dichalcogenides (TMDs) represent a class of semiconducting two-dimensional (2D) materials with exciting properties. In particular, defects in 2D-TMDs and their molecular interactions with the environment can crucially affect their physical and chemical properties. However, mapping the spatial distribution and chemical reactivity of defects in liquid remains a challenge. Here, we demonstrate large area mapping of reactive sulfur-deficient defects in 2D-TMDs in aqueous solutions by coupling single-molecule localization microscopy with fluorescence labeling using thiol chemistry. Our method, reminiscent of PAINT strategies, relies on the specific binding of fluorescent probes hosting a thiol group to sulfur vacancies, allowing localization of the defects with an uncertainty down to 15 nm. Tuning the distance between the fluorophore and the docking thiol site allows us to control Foster resonance energy transfer (FRET) process and reveal grain boundaries and line defects due to the local irregular lattice structure. We further characterize the binding kinetics over a large range of pH conditions, evidencing the reversible adsorption of the thiol probes to the defects with a subsequent transitioning to irreversible binding in basic conditions. Our methodology provides a simple and fast alternative for large-scale mapping of nonradiative defects in 2D materials and can be used for in situ and spatially resolved monitoring of the interaction between chemical agents and defects in 2D materials that has general implications for defect engineering in aqueous condition.