Report Submitted to the Research Experience for Undergraduates Program at the USF College of Engineering. 
 
 

Title:  Heavy Metal Ion Detection Using Peptide-Modified Hydrogel Layers on a Quartz Crystal Microbalance 
 

Name:  Jackie Shepard

Email:  jashepar@eng.usf.edu 

Level: Senior

Number of semesters participated:  3

Date of submission:  May 13, 2005 
 

Advisor:  Dr. Venkat Bhethanabotla

Department:  Chemical Engineering 
 
 
 
 
 
 

This report has been approved:___ Date: 05/10/05     (Advisor signature) 
 

Report can be published on the REU website? YES 

Abstract

      Fabricating a portable, ultra-sensitive sensor would aid in the monitoring of potable water purity.  This can be done by producing a sensor with an “intelligent” component that can selectively test for specific heavy metal ions in aqueous solutions.  A class of peptide/Polymer hybrid thin films can be used to convert ion binding to a detectable viscoelastic change.  The feasibility of synthesizing reproducible, thin layers of poly-NIPAAM on a quartz crystal microbalance (QCM) has been demonstrated.  In addition, viscoelastic changes have been transduced via changes in frequency of the QCM.  These promising results will be applied to finding a relationship between the concentration of heavy metal ions in aqueous solution and the shift in the LCST of the hydrogel network that will occur upon ion binding. 
Introduction

      Detection, analysis, and monitoring of water purity is critical to evaluating toxicity and pollutant levels.  Currently, detection schemes require bulky, expensive instrumentation and componentry such as atomic absorption or fluorimetry.¹  The sample has to be brought into the lab from the field, which could result in lost samples or improper testing.  Another detection method is polarography that provides one of the lowest detection limits of 50 ppt for lead and cadmium.  However, this technique requires the use of mercury.²

      Heavy metals are a major concern in potable water testing.  Heavy metals are toxic even in low concentrations since they accumulate in living organisms.  The United States Environmental Protection Agency (EPA) lists some of the common inorganic

       contaminants:

      Table 1.  EPA drinking water standards³ 
 

Copper, more particularly, is introduced in source water through the water system or corrosion of copper plumbing.  Long-term exposure to copper can cause kidney or liver damage.  Therefore, detection of such contaminants in low concentration is very important.³ 

      A portable, inexpensive sensor for detection of such contaminants would be very beneficial.  It would allow testing to be done out in the field and in more remote areas.  It would do so by developing “intelligent” hydrogel materials that can recognize and communicate ion binding. 
 

Theoretical Background

      A quartz crystal microbalance (QCM) can be used as a sensor due to the piezoelectric effect of the quartz material.  When a mechanical stress is applied to the QCM, an electric response will occur.  Likewise, an electrical stress will cause a Mechanical stress.  The QCM can function as a sensor by detecting a shift in the fundamental resonant frequency of the crystal.⁴

      If an “intelligent” component were applied to the surface of the crystal, it would offer a method of selectively testing for specific ions in water.  The Polymer N-isopropylacrylamide (NIPAAM) embedded w