RESUMO
High-contrast gratings (HCG) are an excellent candidate for label-free detection of various kinds of biomarkers because they exhibit sharp and sensitive optical resonances. In this work, we experimentally show the performance of pedestal HCG (PHCG), which is significantly enhanced in comparison with that of conventional HCG. PCHGs were found to provide a 11.2% improvement in bulk refractive index sensitivity, from 482 nm/RIU for the conventional design to 536 nm/RIU. The observed resonance was narrower, resulting in a higher Q-factor and figure of merit. By depositing Al2O3, HfO2, and TiO2 of different thicknesses as model analyte layers, surface sensitivity values were estimated to be 10.5% better for PHCG. To evaluate the operation of the sensor in solution, avidin was employed as a model analyte. For avidin detection, the surface of the HCG was first silanized and subsequently functionalized with biotin, which is well known for its ability to bind selectively to avidin. A consistent red shift was observed with the addition of each of the functional layers, and the analysis of the spectral shift for various concentrations of avidin made it possible to calculate the limit of detection (LoD) and limit of quantification (LoQ) for the structures. PHCG showed a LoD of 2.1 ng/mL and LoQ of 85 ng/mL, significantly better than the values 3.2 ng/mL and 213 ng/mL respectively, obtained with the conventional HCG. These results demonstrate that the proposed PHCG have great potential for biosensing applications, particularly for detecting and quantifying low analyte concentrations.
RESUMO
Ultrafast excited-state dynamics of CuBr3- complex was studied in acetonitrile and dichloromethane solutions using femtosecond transient absorption spectroscopy with 18 fs temporal resolution and quantum-chemical DFT calculations. Upon 640 nm excitation, the CuBr3- complex is promoted to the ligand-to-metal charge transfer (LMCT) state, which then shortly undergoes internal conversion into the vibrationally hot ligand field (LF) excited state with time constants of 30 and 40 fs in acetonitrile and dichloromethane, respectively. The LF state nonradiatively relaxes into the ground state in 2.6 and 7.3 ps in acetonitrile and dichloromethane, respectively. Internal conversion of the LF state is accompanied by vibrational relaxation that occurs on the same time scale. Based on the analysis of coherent oscillations and quantum-chemical calculations, the predominant forms of the CuBr3- complex in acetonitrile and dichloromethane solutions were revealed. In acetonitrile, the CuBr3- complex exists as [CuBr3(CH3CN)2]-, whereas three forms of this complex, [CuBr3CH2Cl2]-, [CuBr3(CH2Cl2)2]-, and [CuBr3(CH2Cl2)3]-, are present in equilibrium in dichloromethane.
Assuntos
Vibração , Ligantes , Análise EspectralRESUMO
The ultrafast photochemistry of the [Cr(NCS)6]3- complex upon excitation to the 4T2 ligand-field (LF) state was studied in dimethyl sulfoxide (DMSO) and N,N-dimethylformamide (DMF) in a wide temporal range (100 fs to 9 ms) by a combination of femtosecond and nanosecond transient absorption spectroscopy techniques and supported by quantum-chemical DFT/TD-DFT calculations. The initially excited 4T2 state undergoes intersystem crossing to the vibrationally hot 2E state with time constants of 1.1 ± 0.2 and 1.8 ± 0.1 ps in DMSO and DMF, respectively. Vibrational relaxation occurs in the same time scale and takes 1-5 ps. A major part of the [Cr(NCS)6]3- complex in the 2E state undergoes intersystem crossing to the ground state with time constants of 65 ± 5 and 85 ± 5 ns in DMSO and DMF, respectively. A minor part of electronically excited [Cr(NCS)6]3- undergoes irreversible photochemical decomposition. In DMSO, the photolysis of the [Cr(NCS)6]3- complex results in single or double isothiocyanate ion release followed by the coordination of the solvent molecules with a time constant of 1 ± 0.2 ms.
