The aim of our project is to develop a new ultrasensitive method of magnetic measurements based on optimized carbon nanotube electromechanical resonators (CNTERs). More specifically, the CNTERs will be used as force detectors in order to measure the interaction between a magnetic field and a magnetic nanoparticle (MNP) grafted on the nanotube surface. This new and original approach of magnetometry would allow us to perform a direct measurement of the magnetic hysteresis loop of a single nanoparticle chemically synthesized with a magnetic moment below 1000 Bohr magneton (µB) on broad temperature and magnetic field ranges. Since yet, the major part of magnetic studies of nanoparticle elaborated by chemical routes are made on assemblies with macroscopic techniques (SQUID). It implies that the individual properties are hidden or averaged by several distributions, i.e. size, shape and chemical and by the magnetic interaction between nanoparticles. The improvement or the development of new techniques with high sensitivity adapted for objects prepared by chemistry routes remain a fundamental challenge. From a technical point of view, the so called microsquid technique enabled measuring the magnetic properties of a single nanoparticle which magnetic moment is around 1700µB in a limited range of field and temperature. More recently, resonant magnetic force microscopy and magnetotransport measurements succeed in the measure of the single MNP spin dynamics in very peculiar field conditions. CNTERs have a high sensitivity as mass or force sensors as recently demonstrated by the coordinator B. Lassagne. Indeed, carbon nanotubes can measure the weight of a single atom at low temperature which means that they are the most sensitive nanobalance made so far. Thus, CNTERs constitute also the most sensitive force detectors and are excellent candidates to build an ultra sensitive magnetic detector. As a matter of fact, preliminary calculations made by the coordinator show that the current fabricated devices could be used as a magnetic detector with sensitivity as low as few µB at low temperature which would surpass the existing techniques. To our knowledge, this ambitious project has so far no equivalent, neither at the European or international level. One of the main reasons of this singularity is the requirement for a strong collaboration between fields as wide as the physics of carbon nanotube, the chemical synthesis of well-controlled MNPs and the nanomagnetism. The « Laboratoire de Physique et Chimie des Nano-objets » (LPCNO) which regroups chemists and physicist specialists of the chemical synthesis and the magnetic studies of nano-object is well armed to support this project. The objectives of the project are: 1/ the development of highly sensitive CNTERs. 2/ the chemical synthesis of MNP and their addressing onto the CNTER thanks to two different techniques: the electrospray technique and the deposition by nanodispensing of a liquid thanks to a modified atomic force microscopy tip. 3/ magnetometry on a single MNP.