Although there are several aspects that contribute to an efficient chemical sensor system, the choice of responsive materials can help to optimize several key attributes critical for their ultimate performance, specifically high sensitivity, selectivity, fast response time, and wide dynamic range. Some common issues reported to date for sensors are limited detection range, slow response time, long recovery period, and fast saturation (limited dynamic range).[1] Most of these issues are directly related to the large volume of bulk porous material that is needed for measurable signal output, which leads to inherently slow sorption, diffusion, and desorption processes. One type of gas sensor that receives only limited attention despite being among the most frequently used sensors for measuring important environmental quantities is the humidity sensor.[2]Important applications of this type of sensor include for respiratory equipment, incubators, chemical gas purification, and surgical operations. The main requirements for humidity sensors are good sensitivity over a wide humidity range, low hysteresis, good reproducibility, and longevity. [2,3] Often sensors are required to be very small and suitable for integration into arrayed systems, such as odor-sensing arrays. Humidity sensors currently tend to exploit the characteristics of bulk materials with the required resistive and capacitive response properties. This type of sensor comprises a moisture sensitive ceramic, metal, or polymer material that undergoes changes in resistance or capacitance with variations in ambient humidity. [3,4] Water vapor sensors that use polymeric materials commonly incorporate polyimides, polycarbonates, cellulose acetates, or conductive polymers. [5,6] The typical vapor sensitivity of such sensors is of the order of tens of parts per million (or ±0.05 % relative humidity, RH), which is sufficient for most routine measurements. However, this is not acceptable if a fast, real-time monitoring of vapor content variation is required. Increased sensitivity, to a low ppm level, can be achieved using a porous material to maximize the specific surface area available for water vapor adsorption. [7][8][9] For example, 0.4 ppm v (parts per million by volume) water vapor detection was demonstrated by Salonen et al. using carbonized porous silicon.[9] Bruno et al. used a polymer-coated resonant device to obtain a sensitivity of 7 ppm v .[10] In these cases, although the sensors reported showed good sensitivity they suffered sluggish response times, often requiring a few minutes to completely recover. Currently, modest sensitivity and slow response are the main obstacles to the design and development of microcantilever-based sensor technology. [11,12] In this Communication, we present a bimaterial design for humidity sensing with a vapor-sensitive plasma-polymerized nanolayer coating on a silicon microcantilever with a low flexural rigidity (Fig. 1a,d). The coating acts as a sensitive mechanical actuator, which mediates high internal stresses, enabling...

A novel method for the facile fabrication of conformal, ultrathin, and uniform synthetic amino acid coatings on a variety of practical surfaces by plasma-enhanced chemical vapor deposition is introduced. Tyrosine, which is utilized as an agent to reduce gold nanoparticles from solution, is sublimed into the plasma field and directly deposited on a variety of substrates to form a homogeneous, conformal, and robust polyamino acid coating in a one-step, solvent-free process. This approach is applicable to many practical surfaces and allows surface-induced biometallization while avoiding multiple wet-chemistry treatments that can damage many soft materials. Moreover, by placing a mask over the substrate during deposition, the tyrosine coating can be micropatterned. Upon its exposure to a solution of gold chloride, a network of gold nanoparticles forms on the surface, replicating the initial micropattern. This method of templated biometallization is adaptable to a variety of practical inorganic and organic substrates, such as silicon, glass, nitrocellulose, polystyrene, polydimethylsiloxane, polytetrafluoroethylene, polyethylene, and woven silk fibers. No special pretreatment is necessary, and the technique results in a rapid, conformal amino acid coating that can be utilized for further biometallization.

Plasma‐enhanced chemical vapor patterned surfaces are used for site‐ specific attachment of biomolecules and semiconductor quantum dots (QDs; see figure). The fabrication of surfaces with multiple functional building blocks can be used in a single step to create complex multifunctional patterned substrates incorporating self‐assembled monolayers (SAMs) and thiol‐functionalized quantum dots for a variety of applications.

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