Plasmonic nanocone arrays for rapid and detailed cell lysate surface enhanced Raman spectroscopy analysis.

In this work, we develop, fabricate, and characterize a plasmonic nanocone array surface enhanced Raman spectroscopy (SERS) substrate with a uniform enhancement factor on the micron scale for qualitative and quantiative cell and cell lysate analysis. This work demonstrates how SERS substrates can be used as cell-based biosensors given that the enhancement factor of the substrate is sufficient for Raman detection and that the uniformity is high over the applicable surface area. These requirements allow accurate and quantitative comparisons between nonuniform samples under varying biochemical conditions. We apply the developed SERS substrate for Raman measurements and mapping of HeLa cells and cell lysate. This method is used for identification of UV-induced damage and detection of nanomolar concentrations of methylated guanine spiked in cell lysate samples.

Label-free cell-substrate adhesion imaging on plasmonic nanocup arrays.

Cell adhesion is a crucial biological and biomedical parameter defining cell differentiation, cell migration, cell survival, and state of disease. Because of its importance in cellular function, several tools have been developed in order to monitor cell adhesion in response to various biochemical and mechanical cues. However, there remains a need to monitor cell adhesion and cell-substrate separation with a method that allows real-time measurements on accessible equipment. In this article, we present a method to monitor cell-substrate separation at the single cell level using a plasmonic extraordinary optical transmission substrate, which has a high sensitivity to refractive index changes at the metal-dielectric interface. We show how refractive index changes can be detected using intensity peaks in color channel histograms from RGB images taken of the device surface with a brightfield microscope. This allows mapping of the nonuniform refractive index pattern of a single cell cultured on the plasmonic substrate and therefore high-throughput detection of cell-substrate adhesion with observations in real time.

Quantitative phase imaging with partially coherent illumination.

In this Letter, we formulate a mathematical model for predicting experimental outcomes in quantitative phase imaging (QPI) when the illumination field is partially spatially coherent. We derive formulae that apply to QPI and discuss expected results for two classes of QPI experiments: common path and traditional interferometry, under varying degrees of spatial coherence. In particular, our results describe the physical relationship between the spatial coherence of the illuminating field and the halo effect, which is well known in phase-contrast microscopy. We performed experiments relevant to this common situation and found that our theory is in excellent agreement with the data. With this new understanding of the effects of spatial coherence, our formulae offer an avenue for removing halo artifacts from phase images.

Epi-illumination diffraction phase microscopy with white light.

We demonstrate the first reflection-based epi-illumination diffraction phase microscope with white light (epi-wDPM). The epi-wDPM system combines the off-axis, common-path, and white light approaches, in a reflection geometry enabling sub-nanometer spatial and temporal noise levels, while providing single-shot acquisition for opaque samples. We verified the epi-wDPM results by measuring control samples with known dimensions and comparing them to measurements from other well-established techniques. We imaged gold-coated HeLa cells to illustrate the tradeoffs between epi-wDPM with low and high spatial coherence.