Double plasmonic profile of tryptophan–silver nano-crystals—Temperature sensing and laser induced antimicrobial activity

Surface plasmon resonance (SPR) for spherical shaped silver nanoparticles showing double maxima at ∼390 nm and ∼520 nm respectively is reported. Self assembly of silver nanoparticles grown on tryptophan template leads to emergence of equal intensity double plasmon resonance (EIDPR). While for rod shaped nano-forms such double plasmon is explainable but for spherical shaped forms, such double plasmon can be explained on the basis of bidirectional formation of silver cluster in which attachment of silver at two nitrogen atom locations of tryptophan molecule seems to be obligatory. The absence of double resonance in case of silver nanoclusters formed with other amino acids or N-acetyl l-tryptophanamide (NATA), where bidirectional NH2 attachment is not possible, validates the proposed EIDPR mechanism. Electron micrograph of EIDPR particle indicates a bi-periodic fringe pattern indicating unusual crystalline property. Apart from sensing tryptophan, the double plasmon peaks are sensitive to temperature. Furthermore, the particle can be used as a smart killing agent showing bactericidal activity only upon exposure to low power laser.

Graphical abstract.Figure optionsDownload full-size imageDownload high-quality image (142 K)Download as PowerPoint slideHighlights► Double plasmon in spite of spherical shape – the design of the nanostructure is predictable at the molecular level. ► Tryptophan serves as doping substrate that induces bi-periodicity in the nano-crystalline structure as verified in the TEM. ► The particle act as both tryptophan and thermal history sensor. ► The particle shows smart antimicrobial activity.