The current Oddy test, evaluation of potentially damaging museum storage materials, is accomplished by monitoring the tarnish of metal coupons from material off-gassing.  This test, while very useful, is time consuming and difficult to quantify.  Silver is one of the metal coupons used to evaluate the storage materials.  We propose using silver nanoparticles (Ag NPs) to replace the silver metal coupon because of it has the potential of having a  faster reactivity to sulfur emitting compounds and its unique color properties.  Ag NPs have a unique characteristic of exhibiting a significant optical absorbition in the visible wavelengths due to surface plasmon resonance, which is a collective oscillation of  the conduction electrons of Ag NPs in resonance with incident electromagnetic radiation. 

A typical solution of spherical Ag NPs is shown in the image above.  A Ag NP monolayer film can be formed from this colloidal suspension and used as a sensor to detect sulfur gases emitting from museum storage materials.  The films are initially visibly yellow in color and after reacting with sulfur becomes colorless.  Similar to pH sensors that warn of acidic conditions, the NP behaves as a sulfur gas sensor.

The research focus is:

• develop the methodology for making silver nanoparticle monolayer films
• characterize the Ag NPs
• determine the films reactivity with hydrogen sulfide
• evaluate  the sensor when used to monitor the off-gassing of a museum storage material
• compare the results of the sensor to the metal coupons

Ag NP monolayer films were created that are sensitive to hydrogen sulfide gas as well as the sulfur off-gassing from wool materials.  As the reaction proceeded the sensor turned from a yellow to a colorless film.  The reactivity of the film was much faster than a typical metal coupon Oddy test and was easily evaluated through visual inspection.

For more information:
            1.  L. Moussa Master's thesis 2007 (pdf)
             2.  Chen et al. MRS Symp. Proc. 1047 (2007) (in press)

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