In this report we detail our work fabricating and measuring graphene quantum dots. We investigate a technique, relatively widely used in several other materials but not yet well investigated in graphene, known as Atomic Force Microscope Lithography (AFML). We then use AFML to fabricate graphene quantum dot systems. Transport measurements are carried out on our graphene quantum dots at low temperatures and high parallel magnetic fields and we try to understand the behaviour of spins in graphene. In our initial investigations into AFML we use graphene samples electrically contacted using standard electron-beam lithography. We were able to cut the graphene lattice by applying a negative voltage to the AFM tip and moving the tip across a grounded graphene surface. We have shown, by measuring the current through the AFM tip during lithography, that cutting of graphene is not current driven. Using a combination of transport measurements and scanning electron microscopy we show that , while indentations accompanied by tip current appear in the graphene lattice for a range of tip voltages, real cuts are characterized by a strong reduction of the tip current above a threshold voltage. The flexibility of the technique was then demonstrated by the fabrication, measurement, modification and re-measurement of graphene nanodevices with resolution down to 15 nm. We subsequently developed a shadow-masking technique to electrically contact graphene samples thus eliminating the use of chemical resists and the associated contamination of the graphene surface. With these pristine samples we were able to oxidise and hydrogenate the graphene using AFML. A graphene quantum dot was then fabricated using AFML oxidation. We also fabricated a graphene quantum dot using e-beam lithography in combination with oxygen plasma etching. We studied electron spin physics in these structures by J:1pplying large parallel magnetic fields at low temperatures and performing electrical transport measurements. We do not find an ordered filling sequence of spin states, which we assign to edge disorder and surface charge impurities.

Fluorescent carbon dots (C-dots) are well known for their low cell-cytotoxicity, biocompatibility, low preparation cost, excitation dependent photoluminescence, and excellent photostability. Typically, raw C-dots have low quantum efficiency and thus researchers have been utilizing biocompatible polymers such as polyethylene glycol (PEG) as a passivation agent in order to increase fluorescence signal. In this work, we report fluorescent self-passivated carbon nanodots (CNDs) synthesized from PEG by using it as a carbon source as well as a passivating agent. Importantly, the addition of graphene quantum dots (GQDs) during the synthesis of self-passivated CNDs can tune photoluminescence property. The results of bioimaging and cytotoxicity test of self-passivated CNDs hold promises for biomedicine applications.

Philosophiae Doctor - PhD / The main aim of this study was to prepare band gap-engineered graphene quantum dot (GQD) structures which match the different energies of the visible region in the solar spectrum. These band gap-engineered graphene quantum dot structures were used as donor materials in rainbow Schottky junction solar cells, targeting all the energies in the visible region of the solar spectrum for improved solar-to-electricity power conversion efficiency. Structural characterisation of the prepared nanomaterials under solid-state nuclear magnetic resonance spectroscopy (SS-NMR) showed appearance of bands at 40 ppm due to the presence of sp3 hybridised carbon atoms from the peripheral region of the GQD structures. Other bands were observed at 130 ppm due to the presence of polycyclic aromatic carbon atoms from the benzene rings of the GQD backbone, and around 180 ppm due to the presence of carboxylic acid carbons from oxidation due to moisture. Fourier-transform infrared resonance (FTIR) spectroscopy further confirmed the presence of aromatic carbon atoms and oxidised carbons due to the presence of C=O, C=C and -OH functional groups, concurrent with SS-NMR results. / 2023-12-01

No description available.

Doctor of Philosophy / Department of Chemical Engineering / Vikas Berry / Graphene - a single atom thick two dimensional sheet of sp[superscript]2 bonded carbon atoms arranged in a honeycomb lattice - has shown great promise for both fundamental research & applications because of its unique electrical, optical, thermal, mechanical and chemical properties. Derivatization of graphene unlocks a plethora of novel properties unavailable to their pristine parent “graphene”. In this dissertation we have synthesized various structural and chemical derivatives of graphene; characterized them in detail; and leveraged their exotic properties for diverse applications. We have synthesized protein/DNA/ethylenediamine functionalized derivatives of graphene via a HATU catalyzed amide reaction of primary-amine-containing moieties with graphene oxide (GO) – an oxyfunctional graphene derivative. In contrast to non-specificity of graphene, this functionalization of GO has enabled highly specific interactions with analytes. Devices fabricated from the protein (concanavalin – A) and DNA functionalized graphene derivatives were demonstrated to enable label-free, specific detection of bacteria and DNA molecules, respectively, with single quanta sensitivity. Room temperature electrical characterization of the sensors showed a generation of ~ 1400 charge carriers for single bacterium attachment and an increase of 5.6 X 10[superscript]12 charge carriers / cm[superscript]2 for attachment of a single complementary strand of DNA. This work has shown for the first time the viability of graphene for bio-electronics and sensing at single quanta level. Taking the bio-interfacing of graphene to the next level, we demonstrate the instantaneous swaddling of a single live bacterium (Bacillus subtilis) with several hundred sq. micron (~ 600 µm[superscript]2) areal protein-functionalized graphene sheets. The atomic impermeability and high yield strength of graphene resulted in hermetic compartmentalization of bacteria. This enabled preservation of the dimensional and topological characteristics of the bacterium against the degrading effects of harsh environments such as the ultrahigh vacuum (~ 10[superscript]-5 Torr) and high intensity electron beam (~ 150 A/cm[superscript]2) in a transmission electron microscope (TEM) column. While an unwrapped bacterium shrank by ~ 76 % and displayed significant charge buildup in the TEM column; a wrapped bacterium remained uncontracted and undamaged owing to the graphenic wraps. This work has shown for the first time an impermeable graphenic encasement of bacteria and its application in high vacuum TEM imaging without using any lengthy traditional biological TEM sample preparation techniques. In an inch-scale, we fabricated robust free-standing paper composed of TWEEN/Graphene composite which exhibited excellent chemical stability and mechanical strength. This paper displayed excellent biocompatibility towards three mammalian cell lines while inhibiting the non-specific binding of bacteria (Bacillus cereus). We predict this composite and its derivatives to have excellent applications in biomedical engineering for transplant devices, invasive instrument coatings and implants. We also demonstrate a novel, ultra-fast and high yield process for reducing GO to reduced graphene oxide (RGO) using a facile hydride-based chemistry. The RGO sheets thus-produced exhibited high carrier mobilities (~ 100-600 cm[superscript]2/V•s) and reinstatement of the ambipolar characteristic of graphene. Raman spectra and UV-Vis spectroscopy on the RGO sheets displayed a high degree of restoration of the crystalline sp2 lattice with relatively low defects. We fabricated graphene nanoribbons (GNRs) – 1D structural derivatives of graphene – using a nano-scale cutting process from highly oriented pyrolytic graphite (HOPG) blocks, with widths pre-determinable between 5 nm to 600 nm. The as-produced GNRs had very high aspect ratio in the longitudinal direction (~ 0.01); exhibited predominantly mono-layered structure (< 10 % bilayer); and smooth edges (Raman I[subscript]D/G ~ 0.25 -0.28). Low temperature electrical transport measurements on back-gated thin film GNR devices were performed and a carrier mobility of ~ 20 ± 4 cm[superscript]2/V•s with sheet resistances of 2.2-5.1 MΩ / □ was extracted. Despite the ~ 50 nm thicknesses of the films, a clear bandgap scaling was observed with transport via variable range hopping (VRH) in 2 and 3 dimensions. This work demonstrates the first fully functional narrow pristine GNR thin-film field effect transistors (FETs). In addition we fabricated graphene quantum dots (GQDs) – 0D derivatives of graphene with dimensions < 100 nm – using a slight variation of our nano-scale cutting strategy, where the cleavage process is carried out in two dimensions. A high degree of control on the dimensions (Std. Dev. of ~ 5 nm for 50 X 50 nm square GQDs) and shape (pre-determinable between square, rectangle, triangle and trapezoid) of the as-synthesized GQDs is demonstrated. The optical properties of the GQDs such as the UV-Vis absorbance and photoluminescence were studied and their facile tunability was demonstrated depending on their dimensions. This work demonstrates for the first time the high throughput fabrication of GQDs with tunable dimensions and shape.

[pt] O presente trabalho teve como objetivo o desenvolvimento de métodos espectroanalíticos capazes de determinar indiretamente analitos de interesse biológico e farmacológico que possuem fraca atividade óptica no UV-vis (no caso, captopril, histamina e sulfato de canamicina). Embora muitos métodos para quantificar esses analitos estejam reportados, muitos dependem da derivatização química do analito, procedimento considerado complexo e trabalhoso para fazer tais analitos absorverem e emitirem no UV-vis. Por isso, a proposta de uso de pontos quânticos fotoluminescentes é interessante, pois permitem, em condições ajustadas, respostas analíticas que proporcionam a determinação indireta dos analitos de interesse em concentrações da ordem de até 10-8 mol L-1. A determinação do captopril foi proposta utilizando pontos quânticos de grafeno aminofuncionalizados com uso de glutationa (GQDs-amino). O captopril induziu a supressão e o deslocamento espectral (para o vermelho) da fotoluminescência da dispersão aquosa dos GQDs-amino. Por outro lado, quando Fe3+ foi usado como um mediador que gera uma supressão da fotoluminescência da dispersão de GQDs-amino, a adição de captopril restabelece a fotoluminescência original dos pontos quânticos. Em condições experimentais ajustadas, a magnitude da supressão ou de deslocamento espectral da fotoluminescência dos GQDs-amino pode ser relacionada com a concentração de captopril. Em ambos os casos, a resposta linearizada abrangeu três ordens de grandeza (10-6 a 10-4 mol L-1). Em contrapartida, a abordagem de restauração do sinal da sonda, previamente suprimida com Fe3+, também se mostrou útil do ponto de vista analítico. As abordagens propostas foram testadas com a determinação de captopril em amostras simuladas e em formulações farmacêuticas comerciais. O deslocamento 10 espectral a partir da sonda GQDs-amino e ativação/desativação da fotoluminescência utilizando GQDs-amino-Fe3+ resultou em recuperações satisfatórias, mostrando o potencial de detecção quantitativo do método. No estudo com a histamina, avaliou-se o comportamento fotoluminescente da dispersão aquosa de GQDs-amino na presença de histamina com interação mediada por diferentes íons metálicos. Os resultados revelaram que uma interação mais forte e seletiva existia na presença de Eu3+, Fe3+ e Cu2+. A sensibilidade das curvas de supressão de fotoluminescência normalizada (Ks) indicou uma interação dez vezes mais forte da histamina com a superfície dos GQDs na presença de Fe3+. A resposta linear observada nos GQDs-amino-Fe3+ (luminescência medida a 345/435 nm) abrangeu a concentração de histamina de 4,3 × 10-7 mol L-1 (limite de quantificação) até 3,2 × 10-5 mol L-1. A dispersão de GQDs-amino-Fe3+ foi usada como sonda na análise de amostras de atum após extração do analito em cartucho fase sólida catiônica. Os resultados analíticos foram estatisticamente semelhantes aos obtidos com um método baseado na cromatografia líquida com detecção fluorimétrica (após derivatização química da histamina). A determinação do sulfato de canamicina foi feita medindoo efeito que ela exerce sobre a fotoluminescência dos GQDs-amino associados às nanopartículas de ouro (AuNPs), que foram produzidas pela redução de AuCl4 com NaBH4 em uma dispersão aquosa de GQDs-amino (obtido pela pirólise de ácido cítrico e glutationa) contendo também o agente tensoativo catiônico CTAB. O sistema AuNPs-GQDs-amino-CTAB apresentou fotoluminescência suprimida, que foi amplificada na presença de canamicina. Sob condições experimentais ajustadas, a ampliação da fotoluminescência do nanomaterial em função da concentração de analito se mostrou linear e abrangeu três ordens de grandeza (10-7 a 10-5 mol L-1). O uso de extração em fase sólida com um cartucho empacotado com um polímero molecularmente impresso (seletivo para aminoglicosídeos) assegurou a seletividade nas determinações de sulfato de canamicina feitas em vacina da febre amarela e em formula� / [en] The objective of the present work was the development of spectroanalytical methods capable of indirectly determining analytes of biological and pharmacological interest that present inherent weak optical activity in UV-vis (in this case, captopril, histamine and kanamycin sulfate). Although many methods to quantify these analytes are reported, many of these depend on chemical derivatization, a procedure considered complex and laborious to promote UV-vis absorption and luminescence. Therefore, the proposed use of photoluminescent quantum dots is interesting since they allow, under adjusted conditions, analytical responses that allow the indirect determination of the analytes of interest in concentrations of the order of down to 10-8 mol L-1. The determination of captopril was proposed using graphene quantum dots aminofunctionalized using glutathione as a precursor (GQDs-amino). Captopril induced photoluminescence suppression and spectral red-shift from the aqueous dispersion of GQDs-amino. In contrast, when Fe3+ is used as a mediator, it generates a suppression of the photoluminescence of the GQD-amino dispersion and the addition of captopril restored the original photoluminescence of the quantum dots. In adjusted experimental conditions, photoluminescence suppression of the GQDs-amino, as a function of the captopril concentration, can be related both to the magnitude of the suppression and to the spectral shift. In both cases, the linearized response covered three orders of magnitude (10-6 to 10-4 mol L-1). In contrast, the probe signal restoration of the previously Fe3+ suppressed photoluminescent GQDs, also proved to be analytically useful. The proposed approaches were tested by the determination of captopril in simulated samples and in commercial pharmaceutical formulations. Spectral shift from the GQDs-amino probe and the photoluminescence on/off approach (using GQDs-amino-Fe3+ probe) resulted in satisfactory recoveries, showing the quantitative capability of the method. In the work concerning histamine, the photoluminescent behavior of the aqueous dispersion of GQDs-amino in the presence of this amino acid was studied in function of different interaction mediators (metal ions). The results revealed that strong and selective interaction existed in the presence of Eu3+, Fe3+ and Cu2+. The sensitivity of normalized photoluminescence (Ks) suppression curves indicated a ten-fold stronger interaction of histamine with the surface of GQDs in the presence of Fe3+. The linear response observed in the GQDs-amino-Fe3+ (luminescence measured at 345/435 nm) covered the histamine concentration of 4.3 × 10-7 mol L-1 (quantification limit) to 3.2 × 10-5 mol L-1. The GQDs-amino-Fe3+ was applied as a probe in the analysis of tuna fish samples after solid phase extraction (SPE) of the analyte using a cationic solid phase. The analytical results were statistically similar to those obtained with a method based on liquid chromatography with fluorimetric detection (after chemical derivatization of histamine). The determination of kanamycin sulfate was made by measuring the effect it exerts on the photoluminescence of gold nanoparticles (AuNPs) associated GQDs, that were produced by the reduction of AuCl4 with NaBH4 in an aqueous dispersion of GQDs-amino (obtained by pyrolysis of citric acid and glutathione) also containing the cationic surfactant CTAB. The AuNPs-GQDs-amino-CTAB system showed a suppressed photoluminescence, which was amplified in the presence of kanamycin. Under adjusted experimental conditions, the magnification of the photoluminescence of the nanomaterial as a function of the analyte concentration was linear and covered three orders of magnitude (10-7 to 10-5 mol L-1). The use of solid phase extraction with a cartridge packed with a molecularly imprinted polymer (selective for aminoglycosides) ensured selectivity in the determinations made in yellow fever vaccine and in veterinary pharmaceutical formulations. The analytical results were statistically similar to those obtained with an HPLC based method with fluorimetri

Cette étude concerne la caractérisation optique non linéaire (NL) principalement d’ordre 3 dans le visible, l’UV et l’IR en régime picoseconde de différents matériaux tels que certains solvants, le niobate de lithium et les nano-feuilles de graphène. Nous présentons d’abord les expressions des susceptibilités NL. Nous décrivons ensuite la technique de caractérisation Z-scan et ses variantes. Nous présentons une nouvelle méthode qui combine les avantages de Z-scan avec ceux de la microscopie en champ sombre. Nous montrons que cette technique d’imagerie, nommée DFZscan (Dark Field Z-scan), peut mesurer les coefficients de réfraction NL en présence d'une forte absorption NL. Les résultats expérimentaux montrent une importante amélioration de la sensibilité. Finalement, nous comparons les réponses NL des solvants les plus utilisés, dont l’eau qui possède la réfraction NL la plus faible. Ce liquide est utilisé pour caractériser la réponse NL d’une suspension de points quantiques de graphène. Grâce à un modèle simple, nous estimons l'indice de réfraction et d’absorption NL d'une nanofeuille de graphène monocouche. Nous étudions également les non linéarités d’ordres supérieurs dans les matériaux liquides (toluène) et solides (LiNbO3) en vue d’applications potentielles pour la génération de la deuxième harmonique et des modulateurs de guides d'ondes. Ces coefficients peuvent intéresser une grande communauté de chercheurs dans des domaines aussi variés que la filamentation, les solitons, le traitement tout optique du signal et les réseaux de télécommunications. / This study concerns the nonlinear (NL) optical characterization mainly of order 3 in the visible, UV and IR in the picosecond regime of different materials such as solvents, lithium niobate and graphene nanosheets. We first present the expressions of NL susceptibilities. We then describe the Z-scan characterization technique and its variants. We present a new method that combines the advantages of Z-scan with those of dark field microscopy. We show that this imaging technique, called DFZ-scan (Dark Field Z-scan), can measure NL refractive coefficients in the presence of high NL absorption. The experimental results show a significant improvement in the sensitivity. Finally, we compare the NL responses of the most commonly used solvents, including water with the lowest NL refraction. This liquid is used to characterize the NL response of a suspension of graphene quantum dots. Using a simple model, we estimate the refractive index and absorption index NL of a single-layer graphene nanosheet. We also studied higher order non-linearities in liquid (toluene) and solid (LiNbO3) materials for potential applications in second harmonic generation and waveguide modulators. These coefficients can be of interest to a large community of researchers in fields as diverse as filamentation, soliton, all-optical signal processing and telecommunications networks.

[pt] O objetivo deste trabalho foi o desenvolvimento de métodos eletro-analíticos utilizando eletrodos modificados com nanomateriais a base de carbono para determinação de analitos de interesse biológico (creatinina) e farmacológico (primaquina, INHHQ, tiomersal). A determinação de primaquina (antimalárico) e de INHHQ (potencial medicamento para o tratamento de doenças neurodegenerativas) foi proposta usando eletrodo de carbono vítreo (GC) modificado com nanotubos de carbono de paredes múltiplas (MWCNTs) o qual promoveu uma melhora significativa na corrente faradaica e na resolução de pico obtida usando voltametria de onda quadrada (SWV) em tampão Britton-Robinson (BR) 0.02 mol L-1; pH 7.00 e KCl (0.25 mol L-1). Embora vários métodos para quantificar primaquina estejam reportados, muitos deles dependem de procedimentos considerados complexos e trabalhosos, portanto, a modificação proposta de GC usando MWCNTs é comparativamente fácil, levando a uma modificação robusta que produz resultados repetitivos, fornecendo também amplificação do sinal eletroquímico devido à área ativa aumentada e a taxa de transferência eletrônica aprimorada. Os GC/MWCNTs também forneceram, ao trabalhar em um pH adequado, maior resolução na detecção das diferentes etapas eletroquímicas envolvidas no processo redox da primaquina. O eletrodo permitiu o limite de detecção (LOD) de 28 nmol L-1 para a primaquina e, quando associado a um procedimento simples baseado na extração líquido-líquido (LLE) e cromatografia em camada fina (TLC), foi alcançada a seletividade e a capacidade de determinar os níveis mais baixos esperados em amostras de urina. No caso do INHHQ, um método para quantificação por SWV foi relatado pela primeira vez. Além do uso do eletrodo GC/MWCNTs um prévio procedimento de TLC, permitiu a seletividade necessária para determinar o INHHQ no tecido cerebral de ratos Wistar. O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu duas ordens de magnitude (10-6 a 10-5 mol L-1). Os pontos quânticos de grafeno (GQDs) foram escolhidos para modificar quimicamente os eletrodos utilizados para determinar tiomersal e creatinina. GQDs são fragmentos nanométricos de grafeno (presentes em dispersões como monocamada, poucas camadas ou multicamadas) onde o transporte de elétrons é confinado em suas dimensões. GQDs são estruturas baseadas em carbono que são biocompatíveis e apresentam baixa toxicidade. A pesquisa apresenta uma nova abordagem para a determinação de tiomersal (conservante em vacinas e cosméticos) em vacinas contra influenza usando GQDs como modificador do eletrodo de GC e explorando o efeito sinérgico entre GQDs, radiação visível e a diferença de potencial aplicado. Este sistema promove a oxidação do tiomersal, produzindo um aumento significativo na resposta (par redox Hg/Hg2positivo) em termos de intensidade de corrente usando SWV e tampão BR (0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O LOD foi de 0.85 μmol L-1 e a faixa dinâmica linear cobriu três ordens de grandeza (10-6 a 10-4 mol L-1). Para a creatinina (um biomarcador para a disfunção renal), um composto de GQDs-cobre foi usado para modificar um eletrodo de ouro. A determinação da creatinina foi realizada utilizando SWV (tampão BR 0.02 mol L-1; pH 4.00 com KCl a 0.25 mol L-1). O método contou com a diminuição do pico de oxidação Cu/Cu2positivo na presença de creatinina, permitindo LOD de 50 nmol L-1 e faixa dinâmica linear, cobrindo três ordens de magnitude (10-6 a 10-4 mol L-1). A resposta SWV da creatinina foi atribuída à formação do complexo creatinina-Cu2+, sendo razoavelmente seletiva em relação a este analito. Todos os procedimentos desenvolvidos por voltametria foram adequadamente comparados com métodos de referência, sendo estatisticamente compatíveis. / [en] The goal of this work was the development of electro-analytical methods using electrodes modified with carbon-based nanomaterials for determination of analytes of biological (creatinine) and pharmacological interest (primaquine, INHHQ, thiomersal). The determination of primaquine (antimalarial) and INHHQ (potential drug for treatment of neurodegenerative diseases) was proposed using glassy carbon (GC) electrode modified with multi-walled carbon nanotubes (MWCNTs) that promoted significant improvement in faradaic current and better peak resolution obtained using square-wave voltammetry (SWV) in Britton-Robinson (BR) buffer 0.02 mol L-1; pH 7.00 and KCl (0.25 mol L-1). Although several methods to quantify primaquine are reported, many of these depend on procedure considered complex and laborious, therefore, the proposed GC modification using MWCNTs is comparatively easy, leading to a robust modification that produce repetitive results also providing amplification of the electrochemical signal due to the increased active area and improved electron-transfer rate. The GC/MWCNTs also provided, when working on a proper pH, higher resolution in detecting the different electrochemical steps involved in the redox process of primaquine. The electrode enabled limit of detection (LOD) of 28 nmol L-1 for primaquine and, when associated with a simple developed procedure, relying of liquid-liquid extraction (LLE) and thin-layer chromatography (TLC), it was achieved the selectivity and the capability to determine the lower levels expected in urine samples. In the case of INHHQ, a method for quantification by SWV was reported for the first time. In addition to the use of GC/MWCNTs electrode, a previous TLC procedure, enabled the selectivity required to determine INHHQ in brain tissue from Wistar rats. The LOD was 0.85 mol L-1 and the linear dynamic range covered two orders of magnitude (10-6 to 10-5 mol L-1). Graphene quantum dots (GQDs) was chosen to chemically modify electrodes used to determine thiomersal and creatinine. GQDs are nanometric fragments of graphene (present in dispersions as monolayer, few layer or multilayer) where electron transport is confined in their dimensions. GQDs are carbon-based structure that are bio-compatible and present low toxicity. The research presents a new approach for the determination of thimerosal (preservative in vaccines and cosmetics) in influenza vaccines using GQDs as a modifier of the GC electrode and exploring the synergistic effect between GQDs, visible radiation and the applied potential difference. This system promotes thiomersal oxidation, producing a significant increase in response (Hg/Hg2 positive redox pair) in terms of current intensity using SWV and BR buffer (0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The LOD was 0.85 μmol L-1 with linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). For creatinine, a biomarker for the renal dysfunction, a GQDs-copper composite was used to modify a gold electrode. Determination of creatinine was made using SWV (BR buffer 0.02 mol L-1; pH 4.00 with KCl at 0.25 mol L-1). The method relied on the decreasing of the Cu2+/Cu oxidation peak in the presence of creatinine, enabling LOD of 50 nmol L-1 and linear dynamic range covering three orders of magnitude (10-6 to 10-4 mol L-1). The SWV response of creatinine was attributed to the formation of creatinine-Cu2 positive complex being reasonably selective towards this analyte. All procedures developed by voltammetry were adequately compared with reference methods, being statistically compatible.

[pt] Uma sonda fotoluminescente do tipo turn-off foi avaliada para a detecção de Hg(2+) usando pontos quânticos de grafeno (GQDs). Diferentes nanopartículas de carbono fotoluminescentes foram preparadas usando a abordagem bottom-up, usando ácido cítrico ou ácido cítrico misturado com algum composto contendo enxofre (tioureia, tioacetamida ou glutationa). Dispersões desses GQDs foram comparadas em termos de comportamento fotofísico na presença de Hg(2+). Observou-se que as nanopartículas preparadas com ácido cítrico e tioureia (GQDs- TU) apresentaram melhor perfil de supressão fotoluminescente (resposta analítica) na presença de Hg(2+). As condições experimentais foram ajustadas para o melhor perfil de resposta e para obter os parâmetros analíticos de mérito. Um estudo para avaliar possíveis interferências na presença de outros íons de metais pesados além de íons alcalinos e alcalino-terrosos, comumente presentes em amostras de água natural. A curva analítica normalizada (concentração L0/L versus Hg(2+) foi linear (R(2) = 0,998) até 0,20 microgramas L(-1). O limite de quantificação (LOQ) foi de 10 microgramas L(-1) e o limite de detecção (LOD) foi de 3 microgramas L(-1) para o ensaio em batelada. Além disso, a estratégia proposta para a determinação indireta de Hg(2+) foi adaptada para um sistema de análise por injeção em fluxo (FIA). Após a otimização do ensaio, com a faixa linear cobrindo o intervalo até 900 microgramas L(-1) (R(2)= 0,999), os valores de LOD e LOQ foram 24 microgramas L(-1) e 80 microgramas L(-1), respectivamente. A recuperação na amostra simulada de água fortificada foi de 99,4 por cento mais ou menos 1,2. / [en] A photoluminescent turn-off probe was evaluated for the detection of Hg(2+) based on graphene quantum dots (GQDs). Different photoluminescent carbon nanoparticles were prepared using the bottom-up approach, with citric acid and with citric acid mixed with some sulfur compound (thiourea, thioacetamide or glutathione). Dispersions of these GQDs were compared in terms of photophysical behavoior in the presence of Hg(2+) . It was observed that the nanoparticles prepared with citric acid and thiourea (GQDs-TU) presented a better linear photoluminescent suppression (analytical response) in the presence of Hg(2+). Experimental conditions were adjusted to improve analytical response and to obtain analytical figures of merit. A study to evaluate potential interferences in the presence of other heavy metal ions and alkaline and alkaline-earth ions, commonly present in natural water samples. The normalized analytical curve (L0/L versus Hg(2+) concentration) was linear (R(2) = 0.998) up to 0.20 micrograms (L-1). The limit of quantification (LOQ) was 10 micrograms L(-1) and the limit of detection (LOD) was 3 micrograms L(-1) for the batch assay. In addition, the proposed strategy for indirect determination of Hg2+ was applied in a flow injection analysis system (FIA). After optimization of the assay, linear range covered a range up to 900 micrograms L(-1) (R(2) = 0.999) with LOD of 24 micrograms L(-1) and LOQ of 80 micrograms L(-1). The recovery in the fortified water sample was 99.4 percent.

storage devices in micro sizes are receiving more and more attention. One of them, on-paper Microsupercapacitors (MSCs), has become a key energy storage device because of its good mechanical flexibility and high power density. In this project, a triphase system with electrochemically exfoliated graphene and graphene quantum dots to synergistically stabilize PEDOT:PSS in ethylene glycol/water solvent was developed for scalable and reliable inkjet printing. Without any post-treatment, the printed patterns with a large thickness (up to 9 μm, about 0.4 μm per layer) attain a sheet resistance of as low as 4 Ω2−1 and high resolution at a small drop spacing of 10 μm. Thanks to these feature, the areal capacitance of the on-paper MSCs can reach &gt;2 mF cm−2 at a high scan rate of 1000 mV s−1. The device also exhibits excellent mechanical flexibility, long cycle life (&gt;95% capacitance retention after 10000 cycles CV test) and long service time (retain 84% capacitance after 4 months in air without any encapsulation). Moreover, we can directly print the interconnect to connect 4 devices on paper substrate in series or in parallel and thus get rid of metal current collector. / Med den snabba utvecklingen av flexibel och bärbar elektronik får energilagringsenheter i mikrostorlek allt mer uppmärksamhet. En av dem, mikrosuperkondensatorer (MSC) på papper, har blivit en viktig energilagringsenhet på grund av sin goda mekaniska flexibilitet och höga effekttäthet. I det här projektet utvecklades ett trefasigt system med elektrokemiskt exfolierad grafen och grafenkvantprickar för att synergistiskt stabilisera PEDOT:PSS i etylenglykol/vattenlösningsmedel för skalbar och tillförlitlig bläckstråleutskrift. Utan någon efterbehandling uppnår de tryckta mönstren med stor tjocklek (upp till 9 μm, ca 0,4 μmper lager) ett arkmotstånd på så lågt som 4 Ω2−1 och hög upplösning vid ett litet droppavstånd på 10 μm. Tack vare dessa egenskaper kan den ytliga kapacitansen hos MSC på papper nå &gt;2 mF cm−2 vid en hög skanningshastighet på 1000 mV s−1. Anordningen uppvisar också utmärkt mekanisk flexibilitet, lång livslängd (&gt;95% kapacitansbehållning efter 10000 cykler i CV-test) och lång livslängd (behåller 84% kapacitans efter 4 månader i luft utan inkapsling). Dessutom kan vi direkt skriva ut kopplingen för att ansluta fyra enheter på papperssubstratet i serie eller parallellt och på så sätt bli av med metallströmkollektorn.