An alternative to antibodies is the modification of paramagnetic beads with molecules with affinity towards to
target. For example, many antibiotics inhibit bacteria
through binding to peptidoglycan thereby inhibiting growth
(Blecher & Friedman, 2012). This binding property has
been exploited with ferric oxide nanobeads modified with
the antibiotic vancomycin coupled with MALDI-MS
downstream detection. The antibiotic modified beads could
bind both Gram positive and negative bacteria down to
2 log cfu/ml with an analysis time of 60 min (Blecher &
Friedman, 2012). Biosensors have also been described
whereby the phage have been genetically modified to express a biotinylated peptide that is used to couple quantum
dots via a streptavidin bridge. In this instance the quantum
dot acts as a fluorescent label enabling simultaneous capture and detection with a reported sensitivity of 10 cells/
ml