The results of these direct comparisons reveal

The results of these direct comparisons reveal the advantages and disadvantages of each plasmonic transducer and their best applicability. The information about thickness and refractive index of the adsorb layer would be quite useful, because it can be used to determine the density of the adsorbed layers. Thereby, for example, conformational changes of monensin Supplier in the layer could be monitored. Unfortunately, the established plasmonic sensing using gold films yields only the average mass adsorbed on the surface. However, as shown by Hull [13], the conformational changes of proteins can be deduced if there is enough spatial confinement of the plasmon.
Background
Materials and methods
Results and discussion
Conclusion In this work, we experimentally compared the performances of various label-free sensor arrangements based on surface plasmon resonances (propagating and localized) by measuring the same system, which was prepared by well controllable, sequential deposition of charged polyelectrolyte layers. The geometries of the plasmonic transducer were the following: planar gold films (pSPR), ensemble of gold nanoparticles with three different sizes (ensemble lSPR), and single gold particle (single particle lSPR). In order to compare the systems, we defined a signal response Δneff from all the sensors. By analyzing its dependency on the adsorption of thin layers theoretically, we showed that the lSPR signal has a non-linear dependency on the number of deposited layer (opposite to the pSPR), that the signal depends on the size of the nanoparticle pSPR, and that there is a large signal change in comparison to pSPR. This analysis was in agreement with the experimentally measured data. In comparison to pSPR, the highest lSPR signal improvement was in the case of 30nm diameter gold nanoparticle and the first adsorbed layers. Although the background noise of the signal on the pSPR signal was much lower than in the ensemble lSPR, the signal noise during the PEL deposition was governed by the variation of the adsorption process, therefore minimizing this advantage at least for the studied model system. We also showed that it is possible to detect sequential adsorption of PEL layers on an area smaller than 0.02μm2 by the single particle lSPR method. However, in this case the signal noise was substantial larger (around the signal change caused by a single PEL layer). The main reasons for the noise were the lower intensity of the detected scattered light from the single nanoparticle as well as mechanical instability. Further, we used two approaches to yield the thickness and refractive index of the adsorbed layers. We showed that these parameters can be determined either by exploiting the non-linear signal change in lSPR system or by using two different plasmon transducer in lSPR systems,. Although the results were hampered by a certain uncertainty, we suggest using large silver nanoparticles (exhibiting two different plasmon resonances) in lSPR system, which could improve these results.
Conflict of interest
Acknowledgment The project “ImSpec” (FKZ 13N12836), supported by the Federal Ministry of Education and Research (BMBF) Germany, is gratefully acknowledged.
Introduction Breast cancer is the most frequently diagnosed cancer in women worldwide, with nearly 1.4 million new cases annually and the leading cause of cancer death despite the huge progress in treatment [9,25]. Numerous evidences have highlighted the importance of the estrogen receptor (ER) in the progression and invasion of breast cancer cells [28]. Indeed, approximately 70% of new diagnosed breast cancers are ER positive [8]. Estrogen is a hormone playing important roles during mammary gland development but also in the development, risk, and treatment of breast cancer. It mediates its function by binding to and activating both isoforms of estrogen receptors (ERα and ERβ, respectively) in both, membrane and cytoplasm, producing their translocation to nucleus, where ERα, and ERβ are ligand-dependent transcription factors and regulate specific target genes [12]. ERα is the only isoform detectable by immunohistochemistry in breast cancer biopsies and is the predominant subtype expressed in breast tumor tissues. Moreover, recent findings suggest that this steroid receptor transcription factor plays an important role in the biology of breast cancer and drives the proliferation of breast cancer cells [27]. Furthermore, ERα levels in breast tumor samples are highly predictive of a patient\'s response to hormonal therapy [5]. Since ERα is rarely determined in normal breast tissue from women without breast carcinoma and its levels and distribution in biopsies of breast carcinomas are influenced by the age and menopausal status of the patient, well-documented reference ranges are not available [6]. However, a number of biochemical studies have found values of 10fmolmg protein extract (by ligand binding assays) or 15fmolmg protein (by enzyme immunoassays), to discriminate between positive and negative ER tissues [13]. Regarding the serum ERα levels, although clinically significant cut-off values to discriminate between receptor-positive and -negative breast cancer and their prognostic value have not yet been established, Widschwendter et al. [24] found, in a study with 182 breast cancer patients and 188 age-matched controls, that serum ERα bioactivity was associated with the presence of breast cancer and that women with ≥42.1pgmL serum ERα bioactivity had a 2.47-fold risk for breast cancer and 2.70-fold risk for ER-positive breast cancer, respectively. As a result, ERα has been regarded as the most informative valuable marker for the diagnosis and prognosis of breast cancer. Accordingly, the development of new methods for ERα determination together with other breast cancer-associated receptors would benefit the diagnosis and prognosis of breast cancer patients, allowing their stratification in well-defined groups of risk for guided and personalized treatment [16,27].