The absorption spectrum of noble metal spherical nanoparticles is known to be strongly influenced by the dielectric constant of the surrounding material, and as such, these particles are well suited for biosensing applications. To perform biosensing using nanoparticles on a substrate, the metal particles are covalently attached onto quartz using an organic adhesion layer of mercaptosilanes. The particles in solution are characterized by UV-vis spectroscopy and transmission electron microscopy, while those attached to the quartz are characterized with UV-vis spectroscopy and atomic force microscopy. Antibodies are attached to the metal nanoparticles, and the antigen recognition is monitored via the change of light absorption when this binding event occurs. Not only is the absorbance originating from plasmon resonances of the particles influenced by the dielectric properties of molecules attached to the nanospheres but also the interband absorption of the particles changes, which will be demonstrated in this report. A light absorption change is detected when a molecular recognition occurs between the bioreceptor molecules attached to the nanoparticle and a biomolecular counterpart. This change in absorption can be very large when adhered molecules are at resonance (interband transitions). In addition, the presented type of biosensing can be a cost-effective and easy to use alternative to conventional biosensing techniques.

Time-resolved adsorption behavior of a human immunoglobin G (hIgG) protein on a hydrophobized gold surface is investigated using multitechniques:  quartz crystal microbalance/dissipation (QCM-D) technique; combined surface plasmon resonance (SPR) and Love mode surface acoustic wave (SAW) technique; combined QCM-D and atomic force microscopy (AFM) technique. The adsorbed hIgG forms interfacial structures varying in organization from a submonolayer to a multilayer. An “end-on” IgG orientation in the monolayer film, associated with the surface coverage results, does not corroborate with the effective protein thickness determined from SPR/SAW measurements. This inconsistence is interpreted by a deformation effect induced by conformation change. This conformation change is confirmed by QCM-D measurement. Combined SPR/SAW measurements suggest that the adsorbed protein barely contains water after extended contact with the hydrophobic surface. This limited interfacial hydration also contributed to a continuous conformation change in the adsorbed protein layer. The viscoelastic variation associated with interfacial conformation changes induces about 1.5 times overestimation of the mass uptake in the QCM-D measurements. The merit of combined multitechnique measurements is demonstrated.

We assess the validity and advantages of using a quartz crystal microbalance ͑QCM͒ as the metallic-coated substrate used for atomic force microscopy ͑AFM͒ measurements by studying two well-known electrochemical reactions, silver electrodeposition on gold and copper electrodeposition on gold. We compare the results provided by electrochemistry ͑cyclic voltammetry͒, QCM frequency, and damping variations as well as AFM topography, and analyze the advantages of combining the three methods in the same instrument. Comparison of the evolution of the frequency of the third and fifth QCM overtones allows identification of the type of interaction between the sensing electrode and its environment: a rigid layer when the frequency shift is proportional to the overtone number, viscous interaction when the frequency shift is proportional to the square root of the overtone number. This identification scheme leads to results confirmed by the QCM damping.The quartz crystal microbalance ͑QCM͒ is a sensitive technique commonly used for detecting minute mass changes. It is based on an oscillating quartz plate whose resonance frequency varies with the mass adsorbed on the surface of one of the electrodes. It has been used for monitoring electrochemical reactions in a setup simultaneously using the sensing electrode of the QCM as the working electrode ͑WE͒ of the electrochemical setup. [1][2][3] Scanning probe microscopy has been used more recently for monitoring electrodeposition reactions. Electrodeposition of a wide variety of metals including copper and silver has thus been observed with atomic resolution using a scanning tunneling microscope ͑STM͒. 4,5 We have combined in the same instrument a QCM and an atomic force microscope ͑AFM͒. We use this experimental setup to simultaneously measure the mass deposited on the sensing electrode of the QCM ͑as observed by a shift of the resonance frequency of the crystal͒ and the topography of the added layer. 6 In this article we are interested in the morphology of electrodeposited films of silver or copper on gold, and their effect on the sensing mechanism of the QCM. We describe the data analysis procedure leading to a distinction of the type of interaction sensed by the QCM, i.e., rigid layer or viscous layer properties, from the evolution of the frequency of the overtones of the resonator as well as the monitoring of the dissipation ͑being defined as the inverse of the quality factor͒ of the QCM. Thus, simultaneous analysis of the evolution of the frequency of the overtones and damping combined with topography analysis brings complementary information on the interactions of the QCM with its environment, and confirms a previous hypothesis of the discrepancy between predicted and observed mass sensitivities of the quartz crystal resonator, 7,8 namely the major contribution of the interaction with the surrounding viscous liquid and the inadequacy of a rigidbound-mass model for estimating the amount of material interacting with the surface of the QCM. Identifying the conditions in which dif...

ac electrical properties of the heterostructured polymer light-emitting diode consisting of poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylenevinylene] (MEH–PPV) and sodium sulfonated polystyrene (SSPS) ionomer are studied. It is found that the carrier in SSPS is not the ion but the electron, and the conduction mechanism seems to be a space-charge limited current with exponential trap distribution. Based on the results of the impedance analysis, we propose a microscopic model to explain the enhancement of the electroluminescence efficiency of the indium tin oxide/MEH–PPV/SSPS/Al structure.