Analytica Chimica Acta 810 (2014) 86–93 Contents lists available at ScienceDirect Analytica Chimica Acta jou rn al h om epage: www.elsevier.com/locate/aca The influence of film morphology and illumination conditions on the sensitivity of porphyrins-coated ZnO nanorods Gabriele Magna a , Yuvaraj Sivalingam a , Eugenio Martinelli a , Giuseppe Pomarico b , Francesco Basoli b , Roberto Paolesse b , Corrado Di Natale a,∗ a Department of Electronic Engineering, University of Rome Tor Vergata, Rome, Italy b Department of Chemical Science and Technology, University of Rome Tor Vergata, Rome, Italy h i g h l i g h t s • Morphological comparison of two preparations of porphyrins-coated ZnO nanorods. • Contact potential difference mea- sured under different gases and light conditions. • Light enhances the responses and the gain depends on the porphyrin film coverage. • Morphology and light can differ- entiate the sensors sensitivity and selectivity. • PCA shows that PCs capture the inter- actions between VOCs and sensing films. g r a p h i c a l a b s t r a c t a r t i c l e i n f o Article history: Received 24 October 2013 Accepted 3 December 2013 Available online 12 December 2013 Keywords: ZnO nanorods Porphyrins Volatile organic compounds Kelvin probe a b s t r a c t ZnO and porphyrins have complementary properties that make their combination attractive for diverse applications such as photovoltaic and chemical sensing. Among the other features, the organic layer mor- phology is supposed to influence both the chemical sensitivity and the charge transfer processes. In this paper, we studied the influence of the film morphology on the sensing properties by comparing por- phyrins coated ZnO nanorods obtained with two different methods. In the first approach, each porphyrin unit is grafted onto preformed ZnO nanorods by a carboxylic group as linker. The second method is a one-pot procedure, where ZnO nanorods growth occurs in the presence of the water soluble tetrakis-(4- sulfonatophenyl)porphyrin. In both cases the macrocycles share the same Zn-tetraphenylporphyrin core structure, but decorated with different peripheral groups, necessary to comply with the material growth conditions. The adsorption of volatile organic molecules has been monitored measuring the contact potential dif- ference between the sensitive surface and a gold electrode, by means of a Kelvin probe setup. Sensitive signals have been measured both in dark and under visible light. The results show that material prepa- ration affects both the sensitivities to gases and light. A chemometric analysis of four sensors (first and second growth method, measured in dark and in light) shows two main evidences: (a) the interaction ∗ Corresponding author at: Department of Electronic Engineering, University of Rome Tor Vergata, Via del Politecnico 1, 00133 Rome, Italy. Tel.: +39 06 72597348; fax: +39 06 2020519. E-mail addresses: dinatale@uniroma2.it, dinatale@eln.uniroma2.it (C. Di Natale). 0003-2670/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.aca.2013.12.008