Gold nanoparticles enhance fluorescence signals by flow cytometry at low antibody concentrations

Flow cytometry is a universally applied technique in many biological and clinical assays to evaluate cells, bacteria, parasites, and particles at a micrometre scale. More advanced flow cytometers can detect small molecules down to the nanometre scale that may identify intracellular nanostructures. Advancements in the field of nanobiotechnology have led to techniques that allow the study of cellular behaviour after exposure to nanomaterials, particularly, metal nanoparticles. The optical properties of gold nanoparticles regarding surface plasmon resonance (SPR) are established to increase the fluorescence quantum yields of several dyes working as optical antennas, enabling the enhancement of light emission in fluorescent emitters. In this work we constructed a nanoprobe using gold nanoparticles coated with primary antibody Cetuximab. Then, we investigated whether this nanoprobe labelled with secondary fluorescent antibody Alexa Fluor 488, at low concentrations, could promote fluorescent signal enhancement, associated with SPR, and detected by the flow cytometry technique. Our results showed an enhanced fluorescent signal likely due to the proximity between the extinction coefficient of gold nanoparticles and the emission peak of Alexa Fluor 488, at exceptionally low concentrations, occurring within a high level of specificity. Moreover, the nanoprobe did not alter the cellular viability suggesting gold nanoparticles as a feasible approach for cell labelling using low concentrations of secondary antibodies for routine flow cytometry applications.

Salt-induced gold nanoparticles aggregation lights up fluorescence of DNA-silver nanoclusters to monitor dual cancer markers carcinoembryonic antigen and carbohydrate antigen 125

In clinical diagnosis of cancer, the monitoring of single tumor marker may result in many false and missed results, while simultaneous detection of multiple tumor markers should be more accuracy and effective. Here, we report a new strategy that salt-induced gold nanoparticles (AuNPs) aggregation lights up fluorescence of dual-color DNA-silver nanoclusters-aptamer (DNA-AgNCs-apta) for the simultaneous monitoring of carcinoembryonic antigen (CEA) and carbohydrate antigen 125 (CA125). The dual-color aptasensor system is composed of green-emitting DNA-AgNCs with CEA aptamer (gDNA₁-AgNCs-apta₁) and red-emitting DNA-AgNCs with CA125 aptamer (rDNA₂-AgNCs-apta₂) in the ratio of 1:1 in volume. Upon addition of AuNPs, gDNA₁-AgNCs-apta₁ and/or rDNA₂-AgNCs-apta₂ are flexibly adsorbed onto the surface of AuNPs by terminal aptamer(s), which prevents salt-induced AuNPs aggregation under high salt condition and results in fluorescence quenching based on surface plasmon enhanced energy transfer (SPEET). With the addition of CEA and/or CA125, the target(s) and corresponding aptamer(s) coordinate to form the complex, keeping DNA-AgNCs-apta(s) far away from the surface of AuNPs and making AuNPs aggregated in high salt medium. The AuNPs aggregation leads to the recovery of fluorescence signals of DNA-AgNCs-apta(s) due to weakened SPEET. Utilizing the fluorescence aptasensor system, the limit of detection of CEA and CA125 are as low as 7.5 pg·mL^-1 and 0.015 U·mL^-1, respectively. The proposed method can be applied to the selective and simultaneous determination of CEA and CA125 in human serum.

Collective Response in DNA-Stabilized Silver Cluster Assemblies from First-Principles Simulations

We investigate fluorescence resonant energy transfer and concurrent electron dynamics in a pair of DNA-stabilized silver clusters. For this purpose we introduce a methodology for the simulation of collective optoelectronic properties of coupled molecular aggregates starting from first-principles quantum chemistry, which can be further applied to a broad range of coupled molecular systems to study their electro-optical response. Our simulations reveal the existence of low-energy coupled excitonic states, which enable ultrafast energy transport between subunits, and give insight into the origin of the fluorescence signal in coupled DNA-stabilized silver clusters, which have been recently experimentally detected. Hence, we demonstrate the possibility of constructing ultrasmall energy transmission lines and optical converters based on these hybrid molecular systems.