The aim of this study is to locally deposit nanoparticles on an unbiased surface by electroless deposition ͑ED͒ using scanning electrochemical microscopy ͑SECM͒. We have developed an ED process that is based on the reduction of gold ions by hydroquinone ͑H 2 Q͒ and catalyzed by a metallic surface, such as palladium. One of the advantages of this system is the ability to drive the ED at pH 1-7. The metal ions were electrogenerated in a solution consisting of H 2 Q and KCl by anodic dissolution of a gold microelectrode. AuCl 4 − reacted with H 2 Q at the electrolyte/metallic interface to form benzoquinone and gold deposit. The ED has been studied initially in bulk solution containing KCl, H 2 Q, and HAuCl 4 , and then by SECM. We found that the pH had a significant effect on the nature of the deposited gold and could be correlated with the kinetics of gold ions reduction by H 2 Q. Hence, either nanoparticles or much larger crystals could be formed, depending on the pH of the deposition solution. Time of deposition and H 2 Q concentration also affected the shape and density of the deposition.Since the introduction of electroless deposition ͑ED͒ as a plating method for semiconductors and circuit boards by Bell Laboratories, 1 ED has been widely used in the microelectronics industry. 2,3 In this surface catalyzed process, metal ions are reduced by a reducing agent and deposited onto a catalytic substrate without applying an external electric current. A kinetic barrier, which prevents the reduction of the metal ions in the solution, is an essential feature of ED. Over the past 40 years, ED has been used for the deposition of various metals, such as Cu, 4-6 Ag, 7,8 Pt, 9 and Au, 10,11 on unbiased metals and on insulators. Gold plating is relevant in a number of fields because of its high conductivity and chemical stability. Gold ED offers several advantages, including simplicity, processability at low temperature, and coating uniformity. Several studies focusing on Au ED have been reported using different deposition baths. The first autocatalytic gold ED bath consisted of KAu͑CN͒ 2 as the source of gold and KBH 4 or dimethylammine borane ͑DMAB͒, 10 as the reducing agent in a basic solution. 12 Additional baths have been developed based on other reducing agents. For example, Iacovangelo 13 reported a bath for gold plating on nickel using DMAB and hydrazine as reducing agents. Hypophosphite, thiourea, and ascorbic acid have also been employed. 14 All these baths involve basic solutions that are required to increase the thermodynamic driving force of the reducing agents as well as to avoid the evolution of hydrogen cyanide. Therefore, alternative systems using different gold salts ͑e.g., ͓Au͑S 2 O 3 ͒ 2 ͔ 3− ͒ have been developed. 10,11,15,16 Interestingly and in spite of the large number of patents and studies on gold ED, there are only a few reports on the localized ED of gold. Martin and Menon 17 for example produced arrays of gold nanoelectrodes by ED techniques. In their work, a polycarbonate filter membrane ͑10-30 nm...

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Cellobiose dehydrogenase (CDH) is a fascinating extracellular fungal enzyme that consists of two domains, one carrying a flavin adenine dinucleotide (FAD) and the other a cytochrome-type heme b group as cofactors. The two domains are interconnected by a linker and electrons can shuttle from the FAD to the heme group by intramolecular electron transfer. Electron transfer between CDH and an electrode can occur by direct electron transfer (DET) and by mediated electron transfer (MET). This characteristic makes CDH an interesting candidate for integration in systems such as biosensors and biofuel cells. Moreover, it makes CDH an alternative for the reduction of metal ions through DET and MET. In this work we have explored the localized deposition of gold on Pd substrates by CDH through DET and MET. For this purpose we exploited the advantage of scanning electrochemical microscopy (SECM) as a patterning tool. We first demonstrated that gold nanoparticles can be formed in homogenous solution. Then we showed that Au nanoparticles can also be locally formed and deposited on surfaces through DET at low pH and by MET at neutral pH using benzoquinone/hydroquinone as mediator.

Iron corrosion is a complex process that occurs when iron is exposed to oxygen and humidity and is exacerbated by the presence of chloride ions. The deterioration of iron structures or other components can be costly to society and is usually evaluated by following the properties of the corroding material. Here, the iron ions released into solution due to corrosion were detected directly by atomic absorption and their concentration was determined using a calibration curve. Iron corrosion was measured in samples immersed in aqueous solutions that differed in salinity (increasing NaCl concentrations), pH, temperature and presence of oxygen, and under the cathodic protection of a zinc ingot. The corrosion of the iron samples in solution was accelerated by high salinity and temperatures, low pH, the presence of chloride ions and oxygen, and the absence of cathodic protection. Material deterioration due to exposure may be arrested or enhanced by understanding the conditions that expedite the reactions. The experiment was performed by third-year material engineering students and would also be appropriate for an upper-level analytical lab.

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