A method to detect metal-drug complexes and their interactions with pathogenic bacteria via graphene nanosheet assist laser desorption/ionization mass spectrometry and biosensors

A new method was proposed to probe the interactions between transition metals of Fe(II), Fe(III), Cu(II) with a non steroidal anti-inflammatory drug (NSAID), flufenamic acid (FF) using graphene as a matrix for Graphene assisted laser desorption ionization mass spectrometry (GALDI-MS). Metal-drug complexation was confirmed via UV absorption spectroscopy, fluorescence spectroscopy, pH meter, and change in solution conductivity. The optimal molar ratios for these complexation interactions are stoichiometry 1:2 in both Cu(II) and Fe(II) complexes, and 1:3 in Fe(III) complexes at physiological pH (7.4). Metal complexation of the drug could enhance fluorescence for 20 fold which is due to the charge transfer reaction or increase rigidity of the drug. The main interaction between graphene and flufenamic acid is the Pi-Pi interaction which allows us to probe the metal-drug complexation. The GALDI-MS could sensitively detect the drug at m/z 281.0 Da (protonated molecule) with detection limit 2.5 pmol (1.0 mu M) and complexation at m/z 661.0, 654.0 and 933.0 Da corresponding to [Cu(II)(FF)(2)(H2O)(2) + H](+), [Fe(II)(FF)(2)(H2O)(2) + H](+) and [Fe(III)(FF)(3)(H2O)(2) + H](+), respectively (with limit of detection (LOD) 2.0 pmol (10.0 mu M). Matrix assisted laser desorption ionization mass spectrometry (MALDI-MS) spectra show change in the protein profile of intact pathogenic bacteria (Pseudomonas aeroginosa, Staphylococcus aureus). The change in the ionization ability (mainly proton affinity) of pathogenic bacteria may be due to the interactions between the bacteria with the drug (or its complexes). Shielding carboxylic group by metals and increase the confirmed the affinity of the drug and its complexes toward the biological metals. The complexes demonstrated sensitive change of bacteria lysate in the MALDI-MS spectra. The increased demand for high-throughput analysis of pathogenic bacteria attracts us to probe the interaction with drug and its complexes by fluorescence spectroscopy. When the bacteria and the drug (or its complexes) were mixed, the photoluminescence of drug (or its complexes) was enhanced while the bacteria no longer exhibit photoluminescent capability. The fluorescence spectra confirmed the interactions between the pathogenic bacteria with the flufenamic acid (drug) and its metal complexes for highly sensitive detection of bacteria by the proposed biosensor method.