Fabrication of surface modified ZnO nanorod array for MALDI-MS analysis of bacteria in a nanoliter droplet: a multiple function biochip

Abstract

We demonstrated the use of surface modified zinc oxide nanorod (ZnO NR) array chip for on-plate detection, pre-concentration, separation and subsequently matrix-assisted laser desorption/ionization mass spectrometric (MALDI-MS) analysis for bacteria present in nanoliter liquid droplet. The surface modified ZnO NR array can be easily fabricated on Zn foil via chemical method. To explore the potential of the fabricated ZnO NR array chip as a MALDI-MS chip and substrate, standard proteins were studied. It was observed that surface modified ZnO NR array substrates provides significant enhancement on analyte ionization in comparison to the conventional MALDI target plate and efficiently suppress the background noises. This significantly leads to clean mass spectra with high resolution and excellent signal intensity. Furthermore, the proposed method was demonstrated for the analysis of bacteria in nanoliter droplets with high reproducibility and it can be further employed as an effective affinity probe to detect and separate the bacteria from sea water and urine. The lowest detectable concentration of the bacteria cells is 1.9 × 102 cfu μL−1 and the minimum volume required for the sample analysis is 50 nano-liter (nL). We believe that this multiple function biochip can serve as an effective bacteria detecting platform in the near future.