Chromatic Transitions in Polydiacetylene Langmuir‐Blodgett Films due to Molecular Recognition at the Film Surface Studied by Spectroscopic Methods and Surface Analysis

Abstract

Langmuir‐Blodgett films of polydiacetylene are used to create a biosensor on the basis of a surface host‐guest recognition process. Functionalizing a 10 wt.‐% fraction of the diacetylene monomer with biotin leads to a visually observable color change in the resulting polymerized film when streptavidin in the molar ratio streptavidin:biotin = 1:2 is added. The chromatic transition, caused by a shortening of the conjugation length of the π‐electron system in the polydiacetylene backbone, is investigated by monitoring the change of visible optical absorption and Raman spectroscopy. Chemical species and to some extent also the presence of surface‐immobilized peptide are identified via time‐of‐flight secondary‐ion mass spectrometry (TOF‐SIMS) signal assignment and XPS studies.Optical spectra of the blue LB film consisting of two layers PDA 1 and one layer of a mixture containing 10 wt.‐% 7 in 1, the film after 10 min immersion in tris(hydroxymethyl)aminomethane hydrochloride buffer (pH 7.3 at 21 °C) and after 2 h immersion in streptavidin solution (protein:biotin molar ratio = 1:2).magnified imageOptical spectra of the blue LB film consisting of two layers PDA 1 and one layer of a mixture containing 10 wt.‐% 7 in 1, the film after 10 min immersion in tris(hydroxymethyl)aminomethane hydrochloride buffer (pH 7.3 at 21 °C) and after 2 h immersion in streptavidin solution (protein:biotin molar ratio = 1:2).

Polydiacetylene-Coated Sensor Strip for Immunochromatic Detection of Xylella fastidiosa subsp. fastidiosa

“…PDA is a class of amphiphilic lipid polymers known for their unique blue-to-red color transitions in response to stimuli such as high pH, 15,16 high temperature, [17][18][19] and molecular binding events. 20,21 These chromatic properties have resulted in the popular use of PDA in a range of colorimetric biosensing applications in the form of liposomes, [22][23][24] Langmuir-Blodgett films, 25,26 strips, [27][28][29] and others. 30,31 The additional fluorescence "turn-on" characteristic of redphase PDA is attributable to its use in the development of fluorescence-based sensors.…”

Polydiacetylene-coated polyvinylidene fluoride strip aptasensor for colorimetric detection of zinc(II)

“…To date, analyte-specific PDA sensors are mostly developed in the form of a liposome (also referred to as a vesicle) in aqueous solutions [11] , [18] , [19] or a deposited layer on rigid substrate surfaces [20] , [21] , [22] , [23] . However, due to complex sample handling requirements (e.g., multiple pipetting) and high costs of fabrication, these forms are not always ideal for biosensing applications in remote areas or resource-limited settings, which would most benefit from PDA’s instrument-free and naked-eye detection.…”

Aptamer-based cell imaging reagents capable of fluorescence switching

“…Several recent studies have investigated the underlying mechanism behind the observed fluorescence switching, 5b,5g–5j,13 and much of the evidence suggests that this switching is the result of mechanical stress on the PDA structure caused by binding to EpCAM. Such external stresses on the PDA structure are known to trigger electronic transitions in the delocalized π-electron networks of the PDA backbone and thereby change the optical properties.…”

“…In this model, radiative transition (decay) from a higher excited Ag symmetry state (dipole-forbidden) to the lowest excited Bu state (dipole-allowed) is believed to be responsible for shifting the fluorescence wavelength from short (blue) to long (red). 5b,5g–5j,13 We would therefore suppose that direct mechanical interaction between the ACP probes and EpCAM is a necessary requisite for fluorescence switching to occur.…”