Author Correction: Rapid signal enhancement method for nanoprobe-based biosensing.

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Rapid Nanoprobe Signal Enhancement by In Situ Gold Nanoparticle Synthesis.

The use of nanoprobes such as gold, silver, silica or iron-oxide nanoparticles as detection reagents in bioanalytical assays can enable high sensitivity and convenient colorimetric readout. However, high densities of nanoparticles are typically needed for detection. The available synthesis-based enhancement protocols are either limited to gold and silver nanoparticles or rely on precise enzymatic control and optimization. Here, we present a protocol to enhance the colorimetric readout of gold, silver, silica, and iron oxide nanoprobes. It was observed that the colorimetric signal can be improved by up to a 10000-fold factor. The basis for such signal enhancement strategies is the chemical reduction of Au3+ to Au0. There are several chemical reactions that enable the reduction of Au3+ to Au0. In the protocol, Good's buffers and H2O2 are used and it is possible to favor the deposition of Au0 onto the surface of existing nanoprobes, in detriment of the formation of new gold nanoparticles. The protocol consists of the incubation of the microarray with a solution consisting of chloroauric acid and H2O2 in 2-(N-morpholino)ethanesulfonic acid pH 6 buffer following the nanoprobe-based detection assay. The enhancement solution can be applied to paper and glass-based sensors. Moreover, it can be used in commercially available immunoassays as demonstrated by the application of the method to a commercial allergen microarray. The signal development requires less than 5 min of incubation with the enhancement solution and the readout can be assessed by naked eye or low-end image acquisition devices such as a table-top scanner or a digital camera.

Rapid signal enhancement method for nanoprobe-based biosensing.

The introduction of nanomaterials as detection reagents has enabled improved sensitivity and facilitated detection in a variety of bioanalytical assays. However, high nanoprobe densities are typically needed for colorimetric detection and to circumvent this limitation several enhancement protocols have been reported. Nevertheless, there is currently a lack of universal, enzyme-free and versatile methods that can be readily applied to existing as well as new biosensing strategies. The novel method presented here is shown to enhance the signal of gold nanoparticles enabling visual detection of a spot containing <10 nanoparticles. Detection of Protein G on paper arrays was improved by a 100-fold amplification factor in under five minutes of assay time, using IgG-labelled gold, silver, silica and iron oxide nanoprobes. Furthermore, we show that the presented protocol can be applied to a commercial allergen microarray assay, ImmunoCAP ISAC sIgE 112, attaining a good agreement with fluorescent detection when analysing human clinical samples.

Revisiting 30 years of biofunctionalization and surface chemistry of inorganic nanoparticles for nanomedicine.

In the last 30 years we have assisted to a massive advance of nanomaterials in material science. Nanomaterials and structures, in addition to their small size, have properties that differ from those of larger bulk materials, making them ideal for a host of novel applications. The spread of nanotechnology in the last years has been due to the improvement of synthesis and characterization methods on the nanoscale, a field rich in new physical phenomena and synthetic opportunities. In fact, the development of functional nanoparticles has progressed exponentially over the past two decades. This work aims to extensively review 30 years of different strategies of surface modification and functionalization of noble metal (gold) nanoparticles, magnetic nanocrystals and semiconductor nanoparticles, such as quantum dots. The aim of this review is not only to provide in-depth insights into the different biofunctionalization and characterization methods, but also to give an overview of possibilities and limitations of the available nanoparticles.

DNA as a molecular local thermal probe for the analysis of magnetic hyperthermia.

Too hot to handle: The surroundings of magnetic nanoparticles can be heated by applying a magnetic field. Polymer-coated magnetic nanoparticles were functionalized with single-stranded DNA molecules and further hybridized with DNA modified with different fluorophores. By correlating the denaturation profiles of the DNA with the local temperature, temperature gradients for the vicinity of the excited nanoparticles were determined.

Monosaccharides versus PEG-functionalized NPs: influence in the cellular uptake.

Magnetic nanoparticles (NPs) hold great promise for biomedical applications. The core composition and small size of these particles produce superparamagnetic behavior, thus facilitating their use in magnetic resonance imaging and magnetically induced therapeutic hyperthermia. However, the development and control of safe in vivo applications for NPs call for the study of cell-NP interactions and cell viability. Furthermore, as for most biotechnological applications, it is desirable to prevent unspecific cell internalization of these particles. It is also crucial to understand how the surface composition of the NPs affects their internalization capacity. Here, through accurate control over unspecific protein adsorption, size distribution, grafting density, and an extensive physicochemical characterization, we correlated the cytotoxicity and cellular uptake mechanism of 6 nm magnetic NPs coated with several types and various densities of biomolecules, such as glucose, galactose, and poly(ethylene glycol). We found that the density of the grafted molecule was crucial to prevent unspecific uptake of NPs by Vero cells. Surprisingly, the glucose-coated NPs described here showed cellular uptake as a result of lipid raft instead of clathrin-mediated cellular internalization. Moreover, these glucose-functionalized NPs could be one of the first examples of NPs being endocytosed by caveolae that finally end up in the lysosomes. These results reinforce the use of simple carbohydrates as an alternative to PEG molecules for NPs functionalization when cellular uptake is required.