Effects of Center Metals in Porphines on Nanomechanical Gas Sensing.

Huynh Thien Ngo,Kosuke Minami,Genki Yoshikawa,Gaku Imamura,Kota Shiba

doi:10.3390/s18051640

Abstract

Porphyrin is one of the most promising materials for realizing a practical artificial olfactory sensor system. In this study, we focus on non-substituted porphyrins—porphines—as receptor materials of nanomechanical membrane-type surface stress sensors (MSS) to investigate the effect of center metals on gas sensing. By omitting the substituents on the tetrapyrrole macrocycle of porphyrin, the peripheral interference by substituents can be avoided. Zinc, nickel, and iron were chosen for the center metals as these metalloporphines show different properties compared to free-base porphine. The present study revealed that iron insertion enhanced sensitivity to various gases, while zinc and nickel insertion led to equivalent or less sensitivity than free-base porphine. Based on the experimental results, we discuss the role of center metals for gas uptake from the view point of molecular interaction. We also report the high robustness of the iron porphine to humidity, showing the high feasibility of porphine-based nanomechanical sensor devices for practical applications in ambient conditions.

Highlights

Among sensors substituting the five senses, the sensors that can perceive physical stimuli, (e.g., light, sound, and pressure) have been extensively studied and developed
Most of oxygen-containing molecules could bind to the center metal ion in nickel porphyrins with substituents, as the substituents could act as electron withdrawing moieties, which enhanced binding affinity to the axial coordination of nickel [34]
We have studied the properties of porphines and metalloporphines as receptor materials of nanomechanical sensors

Summary

Introduction

Among sensors substituting the five senses, the sensors that can perceive physical stimuli, (e.g., light (eye), sound (ear), and pressure (skin)) have been extensively studied and developed. A sensing platform that meets various requirements such as high sensitivity, compactness, and low power consumption, is needed. For such a platform, we focus on nanomechanical membrane-type surface stress sensors (MSS) [1,2,3,4,5,6,7,8,9]. MSS are composed of thin silicon membranes suspended by four sensing bridges in which piezoresistors (Figure 1, red) are embedded This structure allows highly sensitive electric read-outs of stress/strain induced by the sorption of gas molecules in the receptor layer (Figure 1). Since it has been confirmed that almost all solid materials exhibit mechanical deformation by gas sorption, MSS can detect diverse analytes by utilizing various kinds of materials as a receptor layer

Methods

Results

Conclusion