Bio-nanosensors and communication at the nanoscale are a promising paradigm and technology for the development of a new class of ehealth solutions. While recent communication technologies such as mobile and wireless combined with medical sensors have allowed new successful eHealth applications, another level of innovation is required to deliver scalable and cost-effective solutions via developing devices that operate and communicate directly inside the body. This work presents the application of nano technology for the development of miniaturized bio-nanosensors that are able to communicate and exchange information about sensed molecules or chemical compound concentration and therefore draw a global response in the case of health anomalies. Two communication techniques are reviewed: electromagnetic wireless communication in the terahertz band and molecular communication. The characteristics of these two modes of communication are highlighted, and a general architecture for bio-nanosensors is proposed along with examples of cooperation schemes. An implementation of the bio-nanosensor part of the nanomachine is presented along with some experimental results of sensing biomolecules. Finally, a general example of coordination among bio-nanomachines using both communication technologies is presented, and challenges in terms of communication protocols, data transmission, and coordination among nanomachines are discussed.