While nanotechnology has a wide range of applications, there are certain areas where its use may be limited or not feasible due to various reasons. Some of these areas include:

1. Biological Barriers: Nanoparticles may face challenges when interacting with biological systems. Issues such as biocompatibility, toxicity, and potential adverse effects on living organisms may limit the use of certain nanomaterials in medical applications.

2. Regulatory Concerns: Nanotechnology raises concerns regarding its potential impact on health and the environment. Regulatory agencies may be cautious about approving certain nanomaterials and applications until thorough safety assessments are conducted.

3. Cost Constraints: The production of nanomaterials and nanodevices can be expensive. In some cases, the cost may outweigh the potential benefits, making it economically unviable for widespread use, especially in certain consumer products.

4. Limited Scalability: Some nanotechnologies may face challenges when it comes to scaling up production for mass manufacturing. Processes that work well at the laboratory scale may encounter difficulties when attempting to produce materials or devices on a larger, industrial scale.

5. Ethical and Social Considerations: Nanotechnology raises ethical concerns, especially in areas such as nanomedicine and human augmentation. Issues related to privacy, informed consent, and the potential misuse of nanotechnologies may limit their acceptance in certain applications.

6. Energy Intensive Processes: Certain nanofabrication techniques may require substantial energy inputs. If the energy requirements are too high, it could offset the potential energy savings or environmental benefits of nanotechnology applications.

7. Complexity and Interdisciplinary Challenges: Nanotechnology often requires expertise from various scientific disciplines. The complexity of interdisciplinary research and development may hinder progress in certain applications, especially when collaboration and communication between different fields are challenging.

8. Limited Understanding of Long-Term Effects: In some cases, the long-term effects of exposure to nanomaterials are not fully understood. This lack of knowledge may lead to caution in adopting certain nanotechnologies, especially in areas where potential health and environmental impacts are of concern.

It's important to note that research in nanotechnology is ongoing, and scientists are continually addressing these challenges to expand the applicability of nanotechnology across various fields. As our understanding of nanomaterials and their interactions improves, it may open up new possibilities for applications in areas that are currently considered challenging.