Nano-biospectroscopy

 

Plasmon-enhanced spectroscopy concerns the spectroscopy of enhanced optical responses of molecules in close proximity to plasmonic nanostructures, which results in a strong increase in sensitivity. A main representative of plasmon-enhanced spectroscopies is SERS (surface-enhanced Raman spectroscopy), which offers an ultrasensitive analysis of molecules with fingerprint specificity. SERS detection requires physical or chemical adsorption of a molecular target to a noble metal (typically gold or silver) nanoparticle. Upon excitation of the plasmon resonances of the nanoparticle, a huge electromagnetic field concentrated at its surface dramatically enhances the Raman signal of the adsorbed molecule. In tip-enhanced Raman spectroscopy (TERS) a single 'hot spot' is produced at the end of a sharp metallized tip that can be accurately positioned on the sample surface obtaining Raman analysis with nanometer resolution.

Rapid SERS Ultradetection of Biomolecules

We develop disposable supports comprising plasmonic (gold, silver) nanoparticles (NPs) assembled on cellulose, plastic, glass for rapid and cost-effective SERS analysis of molecules in trace concentration. The unique combination of sensitivity, selectivity and spectral multiplexing of SERS coupled with the use of powerful signal-enhancing assembled NPs represents a valuable option for the sensitive detection of molecules. The support is drop-casted with few microliters of molceule solution and then subjected to a second-to-minute long analysis.   

Advanced SERS activity can be conferred by adding an ultra-thin coating of graphene oxide (GO) tightly adhered to the NPs. The GO@NPs hybrid supports show superior molecule retention and signal reproducibility. 

Exemplary applications include the effective sensing of biomolecules such as proteins, amyloids and biomarkers for early diagnosis of neurodegenerative and cancer diseases. Additionally, the SERS detection may eventually offer a valuable aid for monitoring the disease progress and the response to new treatments.

For more info please contact Martina Banchelli Questo indirizzo email è protetto dagli spambots. È necessario abilitare JavaScript per vederlo..

References:

  1. Martina Banchelli, Bruno Tiribilli, Marella de Angelis, Roberto Pini, Gabriella Caminati, Paolo Matteini Controlled veiling of silver nanocubes with graphene oxide for improved Surface enhcend Raman scattering detection 
    ACS Appl Mater Interfaces 8, 2628-2634 (2016)
  2. Martina Banchelli, Bruno Tiribilli, Roberto Pini, Luigi Dei, Paolo Matteini, Gabriella Caminati Controlled graphene oxide assembly on silver nanocube monolayers for SERS detection: dependence on nanocube packing procedure 
    Beilstein J Nanotechnol 7, 9–21 (2016)

SERS of Proteins in Aqueous Solution

Methods for protein analysis via SERS tipically are based on chemically or physically aggregating noble metal colloids in the presence of the target protein. These methods produce nonuniform distributions of highly localized hot spots conferring scarce reproducibility and severe point-to-point variability. Nonetheless, the processes used for eliciting particle aggregation may cause irreversible denaturation and loss of the native structure and function of the proteins. We propose an alternative approach based on selective and quantitative gathering of protein moelcules at regular hot spots of isolated stabilized silver and silver/gold nanocrystals in acqueous medium at physiological pH. A site-selective strategy assures reproducibility and sensitivity while a high colloidal stability provides SERS detection in physiological buffer. 

The method offers perspectives of highly controlled and reproducible SERS analysis of proteins in their native configuration. 

For more info please contact Paolo Matteini Questo indirizzo email è protetto dagli spambots. È necessario abilitare JavaScript per vederlo..

References:

  1. Paolo Matteini, Maximilien Cottat, Francesco Tavanti, Elizaveta Panfilova, Mario Scuderi, Giuseppe Nicotra, Maria Cristina Menziani, Nikolai Khlebtsov, Marella de Angelis, Roberto Pini Site-Selective Surface-Enhanced Raman Detection of Proteins 
    ACS Nano 
    11(1), 918-926, DOI: 10.1021/acsnano.6b07523 (2017)

FEM Modeling of the E-field 

The nanoscale distribution of the electric field and of the E-field enhancement of a nanocrystal can be obtained by the Finite Element Method (FEM). We realize FEM simulations on plasmonic nanoparticles and nanoparticle clusters in different solvents and with or without the presence of cotings (silica, graphene, polymers) on their surface. 

Exemplary simulations include the continuos E-field distribution on 130 nm-size concave gold nanocubes according to different assemblies and the zone-averaged E-field enhancement factor (EF) over a 50 nm silver nanocube.      

For more info please contact Marella de Angelis Questo indirizzo email è protetto dagli spambots. È necessario abilitare JavaScript per vederlo..

References:

  1. Paolo Matteini, Marella de Angelis, Lorenzo Ulivi, Sonia Centi, Roberto Pini Concave gold nanocubes assemblies as nanotraps for surface-enhanced Raman scattering-based detection of proteins
    Nanoscale 8, 3374-3380 (2015)

Tip-Enhanced Raman Spectroscopy of Pathogenic Amyloids


TERS combines a vibrational information provided by Raman scattering with a signal amplification due to the excitation of the localized surface plasmon resonances (LSPR) in metallic (or metallized) tips. With respect to SERS, in TERS a huge enhancement of the E-field is generated at the tip apex, acting as a highly confined light source that allows for plasmon-enhanced Raman spectroscopy at a single molecule level. By coupling Raman spectroscopy with scanning probe microscopy (SPM) fast topographic imaging and chemostructural sample characterization with sub-nanometer resolution is achieved.

Our research focuses on TERS characterization of biomolecules including misfolded proteins and peptide aggregates. Amyloid oligomers, for example, are precursors of amyloids fibrils and plaques, which are hallmarks of neurodegenerative diseases such as Alzheimer’s. A nanospectroscopy tracking of the evolution of different forms of amyloids can represent a valuable aid to gain insight into the mechanism at the basis of protein misfolding diseases. 

 

Our TERS setup consists of a Renishaw Invia micro-Raman spectrometer coupled to a JPK Nanowizard SENSE Scanning Probe Microscope equipped for AFM. The optical coupling is obtained by means of an optical periscope and an inverted microscope. Thanks to a 5 degrees of freedom AFM (XYZ for the AFM head + XY of the sample holder stage), the tip apex can be accurately positioned in the laser beam focus and scanned over a 100µm2 area of the sample. The sample holder is provided with a fluid cell assuring topographic and spectroscopic imaging also in liquid conditions.

For more info please contact Cristiano D'Andrea Questo indirizzo email è protetto dagli spambots. È necessario abilitare JavaScript per vederlo..

 

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