Detection of hexanal and 1-octen-3-ol in refrigerated grass carp fillets using a QCM gas sensor based on hydrophobic Cu(I)-Cys nanocomposite

Hexanal and 1-octen-3-ol have been identified previously as freshness indicators of refrigerated (4 degrees C) grass carp fillets and increase from 0 day to 4 days. Thus, a novel quartz crystal microbalance (QCM) gas sensor was fabricated for hexanal and -1-octen-3-ol detection at room temperature with a hydrophobic cysteine sensitized Cu2O (Cu(I)-Cys) nanocomposite as the sensing layer. The QCM gas sensor coated with 10 mu L of the hydrophobic Cu(I)-Cys nanocomposite for each side exhibited good reproducibility, hydrophobicity, reversibility, sensitivity, selectivity and stability towards hexanal and 1-octen-3-ol under 80 % RH. The sensing mechanism of the sensor towards hexanal and 1-octen-3-ol was proposed as (1) resistance to water vapor by hydrophobic silica nanoparticles; (2) formation of sulfhydryl compound between cysteine and Cu2O nano cubes; (3) hydrogen bonding interaction between cysteine's carboxyl group and hexanal (Delta H =-45.2 kJ/mol) as well as cysteine's amino group and 1-octen-3-ol (Delta H =-60.3 kJ/mol) based on Gaussian calculation results. This hydrophobic Cu(I)Cys nanocomposite based QCM gas sensor was applied to discriminate refrigerated grass carp fillets within 4 storage days. Validation of the proposed sensor was carried out by correlating the frequency shifts with the contents of hexanal and 1-octen-3-ol obtained from solid phase micro extraction-gas chromatography mass spectrometer (SPME-GCMS). The sensor responses showed a good congruence with the SPME-GCMS analysis with a correlation coefficient of 0.96.